Patent Description:
Polylactate (polylactide or polylactic acid) resin is a plant-derived resin obtained from plants such as corn, etc., and is attracting attention as an environment-friendly material having excellent tensile strength and elastic modulus while having biodegradable properties. Specifically, unlike petroleum-based resins such as polystyrene resin, polyvinyl chloride (PVC) resin, polyethylene, etc., which are currently used, polylactate resin has effects of preventing the depletion of petroleum resources, suppressing carbon dioxide emissions, etc., and thus it can reduce environmental pollution, which is a drawback of petroleum-based plastic products. Therefore, as the problem of environmental pollution caused by waste plastic, etc. has emerged as a social problem, it has been attempted to expand the scope of application to the fields of the products where general plastics (petroleum-based resins) were used, such as food packaging materials and containers, electronic product cases, etc..

However, the polylactate resin has low impact resistance and heat resistance, as compared with existing petroleum-based resins, and thus its application range is limited. Further, the polylactate resin has poor elongation characteristics and easily exhibits brittleness, which has a limitation as a general-purpose resin.

Accordingly, to enhance the elongation characteristics of the polylactate resin, a method of compounding an additive or forming a copolymer with a functional monomer, or to enhance heat resistance, a method of adding a nucleating agent or an inorganic additive, etc. has been proposed. However, the additives used in these methods have a problem in that most of them are not biodegradable.

Accordingly, it is required to develop a material exhibiting improved heat resistance and elongation characteristics while maintaining biodegradability.

<CIT> discloses a polylactic acid stereocomplex resin composition comprising a crystalline poly L-lactic acid and a crystalline poly D-lactic acid having a weight average molecular weight of <NUM>,<NUM> to <NUM>,<NUM>; and a method for preparing the composition, wherein the polylactic acid is a polyester-based resin manufactured by an esterification reaction using a lactic acid monomer.

<NPL>, discloses poly(<NUM>-hydroxyalkanoate)-b-poly(D,L)-lactide diblock copolymer.

There are provided a polylactate stereocomplex having improved heat resistance and elongation characteristics while maintaining biodegradability, and a preparation method thereof.

According to one aspect of the present invention, provided is a polylactate stereocomplex including:.

According to another aspect of the present invention, provided is a method of preparing a polylactate stereocomplex, the method including the step of mixing a poly(L-lactate-<NUM>-hydroxypropionate) block copolymer including <NUM> parts by weight to <NUM> parts by weight of a poly(<NUM>-hydroxypropionate) repeating unit with respect to <NUM> parts by weight of a poly(L-lactate) repeating unit and a poly(D-lactate) having a weight average molecular weight of <NUM>,<NUM>/mol or more to less than <NUM>,<NUM>/mol.

A polylactate stereocomplex of the present invention may have excellent physical properties such as heat resistance, elongation characteristics, etc. while maintaining biodegradability, thereby being suitably used as an eco-friendly general-purpose resin.

The terms used in this description are just for explaining exemplary embodiments and it is not intended to restrict the present invention. The singular expression may include the plural expression unless it is differently expressed contextually. It must be understood that the term "include", "equip", or "have" in the present description is only used for designating the existence of characteristics taken effect, steps, components, or combinations thereof, and do not exclude the existence or the possibility of addition of one or more different characteristics, steps, components or combinations thereof beforehand.

As used herein, the "poly(L-lactate-<NUM>-hydroxypropionate) block copolymer" refers to a block copolymer including a poly(L-lactate) repeating unit derived from an L-lactic acid monomer and/or an L-lactide monomer and a poly(<NUM>-hydroxypropionate) repeating unit derived from a <NUM>-hydroxypropionate monomer, and may be expressed as "P(LLA-<NUM>-HP) block copolymer", or "P(LLA-b-<NUM>-HP)".

Further, as used herein, the "poly(L-lactate)" is a homopolymer of an L-lactate monomer and/or an L-lactide monomer, and may be expressed as "PLLA", and the "poly(D-lactate)" is a homopolymer of a D-lactic acid monomer and/or a D-lactide monomer, and may be expressed as "PDLA".

Polylactate resin has biodegradability and biocompatibility, and thus is used as a representative biodegradable resin. However, it exhibits low thermal stability and elongation, which limits its use as a general-purpose alternative resin to polyolefin.

Accordingly, the present inventors have continued to study a material having excellent heat resistance and elongation characteristics while maintaining biodegradability, and as a result, they found that a poly(L-lactate-<NUM>-hydroxypropionate) block copolymer satisfying <NUM> parts by weight to <NUM> parts by weight of a poly(<NUM>-hydroxypropionate) repeating unit with respect to <NUM> parts by weight of a poly(L-lactate) repeating unit is able to form a stereocomplex with poly(D-lactate), and this polylactate stereocomplex has remarkably improved heat resistance and elongation characteristics, as compared with the existing polylactate resins, thereby completing the present invention.

According to one aspect of the present invention, provided is a polylactate stereocomplex including a poly(L-lactate-<NUM>-hydroxypropionate) block copolymer including <NUM> parts by weight to <NUM> parts by weight of a poly(<NUM>-hydroxypropionate) repeating unit with respect to <NUM> parts by weight of a poly(L-lactate) repeating unit; and a poly(D-lactate) having a weight average molecular weight of <NUM>,<NUM>/mol or more to less than <NUM>,<NUM>/mol.

The poly(L-lactate-<NUM>-hydroxypropionate) block copolymer may exhibit excellent flexibility and tensile property due to the poly(<NUM>-hydroxypropionate) repeating unit, as compared with a poly(L-lactate) homopolymer, while maintaining crystallinity of the poly(L-lactate) repeating unit, thereby forming the stereocomplex with poly(D-lactate).

In other words, the poly(L-lactate) in the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer may bind with the poly(D-lactate) like a zipper through an intermolecular bond such as a hydrogen bond, etc., and as a result, the polylactate stereocomplex of the present invention may exhibit excellent thermal stability and elongation characteristics.

To meet the above characteristics, the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer of the present invention may preferably include <NUM> parts by weight or more to <NUM> parts by weight or less, for example, <NUM> parts by weight or more, or <NUM> parts by weight or more, and <NUM> parts by weight or less, or <NUM> parts by weight or less, or <NUM> parts by weight or less of the poly(<NUM>-hydroxypropionate) repeating unit with respect to <NUM> parts by weight of the poly(L-lactate) repeating unit.

When the content of the poly(<NUM>-hydroxypropionate) repeating unit is less than <NUM> parts by weight with respect to <NUM> parts by weight of the poly(L-lactate) repeating unit, it is difficult to secure the effect of improving physical properties of the polylactate stereocomplex, such as elongation, etc. When the content thereof is <NUM> parts by weight or more, the formation rate of the stereocomplex with poly(D-lactate) may be greatly reduced.

Meanwhile, the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer may have a weight average molecular weight of <NUM>,<NUM>/mol or more, or <NUM>,<NUM>/mol or more, or <NUM>,<NUM>/mol or more, and <NUM>,<NUM>/mol or less, or <NUM>,<NUM>/mol or less, or <NUM>,<NUM>/mol, or less, or <NUM>,<NUM>/mol or less.

When the weight average molecular weight of the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer is less than <NUM>,<NUM>/mol, it is difficult to obtain sufficient strength when the stereocomplex is formed. Further, when the weight average molecular weight of the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer is more than <NUM>,<NUM>/mol, there is a problem in that processing becomes difficult, and thus it is preferable to meet the above range.

Further, the poly(L-lactate-<NUM> -hydroxypropionate) block copolymer may have a melting temperature (Tm) of <NUM> or higher, <NUM> or higher, or <NUM> or higher. The melting temperature of the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer may be, for example, <NUM> or lower.

The poly(L-lactate-<NUM>-hydroxypropionate) block copolymer meeting the content of the poly(<NUM>-hydroxypropionate) repeating unit may be prepared by the step of forming the poly(L-lactate) repeating unit and the poly(<NUM>-hydroxypropionate) repeating unit by ring-opening polymerization of the L-lactide monomer in the presence of a poly(<NUM>-hydroxypropionate) initiator.

At this time, the poly(<NUM>-hydroxypropionate) initiator may preferably have a weight average molecular weight of <NUM>,<NUM>/mol to <NUM>,<NUM>/mol, <NUM>,<NUM>/mol to <NUM>,<NUM>/mol, <NUM>,<NUM>/mol to <NUM>,<NUM>/mol, or <NUM>,<NUM>/mol to <NUM>,<NUM>/mol in order to allow the block copolymer to exhibit excellent physical properties without deterioration in the polymerization activity.

The poly(L-lactate-<NUM>-hydroxypropionate) block copolymer prepared from the poly(<NUM>-hydroxypropionate) initiator meeting the above molecular weight range may maintain crystallinity of the poly(L-lactate) repeating unit (block), thereby forming a stereocomplex with the poly(D-lactate).

A method of preparing the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer suitable for formation of the polylactate stereocomplex of the present invention will be described in more detail in a description of a method of preparing the polylactate stereocomplex.

The poly(D-lactate) which forms the stereocomplex with the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer is a homopolymer of a D-lactic acid monomer and/or a D-lactide monomer, and may have an optical purity of <NUM>% or more, <NUM>% or more, or <NUM>% or more.

The poly(D-lactate) may preferably have a weight average molecular weight of <NUM>,<NUM>/mol or more, or <NUM>,<NUM>/mol or more, or <NUM>,<NUM>/mol or more, or <NUM>,<NUM>/mol or more, and <NUM>,<NUM>/mol or less, <NUM>,<NUM>/mol or less, or <NUM>,<NUM>/mol or less. When the weight average molecular weight of the poly(D-lactate) is less than <NUM>,<NUM>/mol, there is a problem in that it is difficult to have sufficient crystallinity. When the weight average molecular weight of the poly(D-lactate) is more than <NUM>,<NUM>/mol, it is difficult to achieve the effects of the present invention due to remarkable deterioration in the tensile and elongation characteristics of the prepared stereocomplex, and for this reason, it is preferable to meet the above range.

The weight average molecular weights of the poly(<NUM>-hydroxypropionate) initiator, the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer, and the poly(D-lactate) may be measured by gel permeation chromatography (GPC) as in Examples described below.

The polylactate stereocomplex may include <NUM> parts by weight to <NUM> parts by weight of the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer; and <NUM> parts by weight to <NUM> parts by weight of the poly(D-lactate). As described, when the content of the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer is high, mechanical properties of the prepared polylactate stereocomplex may be further improved. More preferably, the polylactate stereocomplex may include <NUM> parts by weight to <NUM> parts by weight of the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer; and <NUM> parts by weight to <NUM> parts by weight of the poly(D-lactate).

The polylactate stereocomplex of the present invention exhibits remarkably improved heat resistance and elongation characteristics, as compared with the existing polylactate resins, because the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer and the poly(D-lactate) form the complex, as described.

Specifically, the polylactate stereocomplex may have a melting temperature (Tm) of <NUM> or higher, and <NUM> or lower, <NUM> or lower, <NUM> or lower, or <NUM> or lower.

When the melting temperature is <NUM> or higher, it may be determined that the polylactate stereocomplex has been formed. At this time, as a melting enthalpy is higher, it may be determined that the formation rate of the stereocomplex, i.e., the ratio of each polymer participating in the formation of the stereocomplex is higher. Accordingly, the polylactate stereocomplex according to one embodiment of the present invention may have a melting enthalpy of <NUM> J/g or more, or <NUM> J/g or more, and <NUM> J/g or less, or <NUM> J/g or less.

The melting temperature and the melting enthalpy may be measured by differential scanning calorimetry.

Meanwhile, the polylactate stereocomplex may have elongation of <NUM> % or more, <NUM> % or more, or <NUM> % or more, as measured in accordance with IPC-TM-<NUM> using a tensile strength tester after preparing a dogbone-shaped test specimen of ASTM D638 Type V, indicating that the polylactate stereocomplex exhibits remarkably excellent elongation, as compared with the existing stereocomplex of poly(L-lactate) and poly(D-lactate). The upper limit of the elongation may be, but is not particularly limited to, for example, <NUM> % or less, or <NUM>% or less.

Methods of measuring the melting temperature, the melting enthalpy, and the elongation characteristics of the polylactate stereocomplex will be described in more detail in Examples below.

Meanwhile, according to another aspect of the present invention, provided is a method of preparing the above-described polylactate stereocomplex.

Specifically, the polylactate stereocomplex may be prepared by a preparation method including the step of mixing a poly(L-lactate-<NUM>-hydroxypropionate) block copolymer including <NUM> parts by weight to <NUM> parts by weight of a poly(<NUM>-hydroxypropionate) repeating unit with respect to <NUM> parts by weight of a poly(L-lactate) repeating unit and a poly(D-lactate).

Features of the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer and the poly(D-lactate) are the same as described above.

Methods of preparing the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer and the poly(D-lactate) are not particularly limited, and known methods may be applied.

For example, the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer may be prepared by the step of forming the poly(L-lactate) repeating unit and poly(<NUM>-hydroxypropionate) repeating unit by ring-opening polymerization of the L-lactide monomer in the presence of a poly(<NUM>-hydroxypropionate) initiator.

The poly(<NUM>-hydroxypropionate) initiator includes a hydroxy group and/or an alkoxy group at the end. Thus, when the poly(<NUM>-hydroxypropionate) initiator is added to the ring-opening polymerization reaction of the lactide monomer, the lactide monomer starts to be inserted from the end of the poly(<NUM>-hydroxypropionate) initiator, and as a result, the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer may be prepared.

Therefore, when the ring-opening polymerization reaction of the lactide monomer is performed in the presence of the poly(<NUM>-hydroxypropionate) initiator, the poly(<NUM>-hydroxypropionate) serves as a polymerization initiator, and at the same time, is included as a repeating unit in the block copolymer, thereby making it possible to improve mechanical properties of the finally prepared block copolymer, such as flexibility, impact strength, etc. Specifically, since the poly(<NUM>-hydroxypropionate) is included in the finally prepared block copolymer, it is possible to lower a glass transition temperature (Tg) of the block copolymer, thereby increasing the flexibility.

In this regard, an input amount of the poly(<NUM>-hydroxypropionate) initiator may be selected within an appropriate range in consideration of the content of the repeating unit of poly(<NUM>-hydroxypropionate) included in the finally prepared block copolymer and a molar ratio of the hydroxy group and/or alkoxy group of the initiator which is required to initiate the minimum polymerization.

Specifically, in consideration of the minimum content for maintaining crystallinity of the poly(L-lactate) repeating unit of the finally prepared block copolymer while optimizing the flexibility and mechanical properties thereof, and for acting as an initiator of the ring-opening polymerization reaction, the poly(<NUM>-hydroxypropionate) initiator may be added in an amount of <NUM> parts by weight or more, or <NUM> parts by weight or more, and <NUM> parts by weight or less, or <NUM> parts by weight or less with respect to <NUM> parts by weight of the L-lactide monomer.

The poly(<NUM>-hydroxypropionate) initiator may have a weight average molecular weight of <NUM>,<NUM>/mol to <NUM>,<NUM>/mol, <NUM>,<NUM>/mol to <NUM>,<NUM>/mol, <NUM>,<NUM>/mol to <NUM>,<NUM>/mol, or <NUM>,<NUM>/mol to <NUM>,<NUM>/mol in order to exhibit excellent physical properties of the block copolymer without deteriorating polymerization activity. When the weight average molecular weight of the poly(<NUM>-hydroxypropionate) initiator is less than <NUM>,<NUM>/mol, the content of poly(<NUM>-hydroxypropionate) may be reduced, and when the weight average molecular weight is more than <NUM>,<NUM>/mol, the polymerization activity may be reduced.

On the other hand, before the ring-opening polymerization step, <NUM>-hydroxypropionate may be subjected to a condensation polymerization to prepare the poly(<NUM>-hydroxypropionate) initiator. The reactant including the prepared poly(<NUM>-hydroxypropionate) initiator and lactide monomer is dried, and then the dried poly(<NUM>-hydroxypropionate) initiator and lactide monomer may be subjected to a ring-opening polymerization to prepare the above-mentioned block copolymer.

As the catalyst used in the ring-opening polymerization, all catalysts generally used in the preparation of polylactate resins by ring-opening polymerization of lactide monomers may be used. For example, the ring-opening polymerization may be performed in the presence of one or more catalysts selected from the group consisting of an organometallic complex catalyst and an organic catalyst.

The organometallic complex catalyst may be used without limitation in its composition, as long as it is generally used for preparing polylactate resins by ring-opening polymerization of lactide monomers. For example, the organometallic complex catalyst may be a catalyst represented by the following Chemical Formula <NUM>:.

[Chemical Formula <NUM>]     MA<NUM>pA<NUM><NUM>-p.

in Chemical Formula <NUM>, M is Al, Mg, Zn, Ca, Sn, Fe, Y, Sm, Lu, Ti, or Zr, p is an integer of <NUM> to <NUM>, and A<NUM> and A<NUM> are each independently an alkoxy or carboxyl group.

More specifically, MA<NUM>pA<NUM><NUM>-p may be tin (II) <NUM>-ethylhexanoate (Sn(Oct)<NUM>).

On the other hand, the organic catalyst may be used without limitation in its composition as long as it is generally used for preparing polylactate resins by ring-opening polymerization reaction of lactide monomers. For example, the organic catalyst may be one or more selected from the group consisting of the following <NUM>,<NUM>,<NUM>-triazobicyclo-[<NUM>,<NUM>,<NUM>]dec-<NUM>-ene (TBD), the following <NUM>,<NUM>-diazabicyclo[<NUM>. <NUM>]undec-<NUM>-ene (DBU), the following <NUM>-methyl-<NUM>,<NUM>,<NUM>-triazabicyclo[<NUM>. <NUM>] dec-<NUM>-ene (MTBD), the following <NUM>-dimethylaminopyridine (DMAP), the following <NUM>-(<NUM>-pyrrolidinyl)pyridine (PPY), imidazole, triazolium, thiourea, tertiary amine, and creatinine.

The imidazole may be one or more selected from the group consisting of the following compounds. <CHM>
<CHM>.

The triazolium may be the following compound.

The thiourea may be one or more selected from the group consisting of the following compounds.

The tertiary amine may be one or more selected from the group consisting of the following compounds.

When the lactide ring-opening polymerization reaction proceeds in the presence of the above-mentioned catalyst, depolymerization or decomposition of the finally prepared block copolymer may be suppressed, and a poly(L-lactate-<NUM>-hydroxypropionate) block copolymer having a higher molecular weight and excellent mechanical properties may be obtained with a higher conversion rate.

In the method of preparing the block copolymer according to an aspect, the content of the catalyst may be <NUM> mol% to <NUM> mol%, <NUM> mol% to <NUM> mol%, <NUM> mol% to <NUM> mol%, or <NUM> mol% to <NUM> mol% with respect to <NUM> mol% of the lactide monomer. When the content of the catalyst is less than <NUM> mol% with respect to <NUM> mol% of the lactide monomer, polymerization activity may not be sufficient, and when the content of the catalyst is more than <NUM> mol%, the residual catalyst amount of the prepared poly(L-lactate-<NUM>-hydroxypropionate) block copolymer becomes larger, which may lead to decomposition or molecular weight reduction of the copolymer due to depolymerization such as transesterification reaction, etc..

The ring-opening polymerization may be performed at <NUM> to <NUM> for <NUM> minutes to <NUM> hours.

Further, the ring-opening polymerization reaction may be performed by bulk polymerization using substantially no solvent. At this time, "using substantially no solvent" may cover the case of using a small amount of a solvent for dissolving the catalyst, for example, the case of using up to less than <NUM> of the solvent per <NUM> of the used lactide monomer. As the ring-opening polymerization proceeds by bulk polymerization, it becomes possible to omit a process of removing the solvent after polymerization, and decomposition or loss of the resin in such a solvent removal process may also be suppressed. In addition, by the bulk polymerization, the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer may be obtained with high conversion and yield.

The poly(L-lactate-<NUM>-hydroxypropionate) block copolymer prepared as above maintains crystallinity of the poly(L-lactate) repeating unit, thereby forming the polylactate stereocomplex by polymerization with the poly(D-lactate).

Meanwhile, the poly(D-lactate) may be a commercially available product, or may be prepared according to a known synthetic method. In one embodiment, the poly(D-lactate) may be prepared by condensation polymerization of a D-lactic acid monomer in the presence of a catalyst.

Next, the poly(L-lactate-<NUM>-hydroxypropionate) block copolymer may be mixed with the poly(D-lactate) to prepare the stereocomplex. At this time, a melt compounding method may be used, and in this case, a molecular weight of the prepared polylactate stereocomplex may be rather reduced. However, the stereocomplex may be formed within a short time, and the formation rate of the complex may be high.

The melt compounding may be performed at a temperature of <NUM> to <NUM>, or <NUM> to <NUM>, or <NUM> to <NUM>. When the temperature during the melt compounding is lower than <NUM>, the formation rate of the stereocomplex may be lowered. When the temperature is excessively high by exceeding <NUM>, the polymer may be thermally deformed, and thus it is preferable to meet the above-mentioned range. The melt compounding may be performed at atmospheric pressure, i.e., within a pressure range of <NUM> Torr to <NUM> Torr. The poly(L-lactate-<NUM>-hydroxypropionate) block copolymer and the poly(D-lactate) may be stirred under the above temperature and pressure conditions for <NUM> minutes or more, or <NUM> minutes to <NUM> hour to prepare the polylactate stereocomplex.

Hereinafter, preferred exemplary embodiments will be provided for better understanding of the present invention. However, the following exemplary embodiments are only for illustrating the present invention.

<NUM> (<NUM> mmol) of <NUM>-hydroxypropionate was dried, and then subjected to condensation polymerization in the presence of <NUM> of a p-toluene sulfonic acid (p-TSA) catalyst under conditions of a temperature of <NUM> and a reduced pressure of <NUM> Torr for <NUM> hours to prepare a poly(<NUM>-hydroxypropionate) oligomer.

A weight average molecular weight of the prepared poly(<NUM>-hydroxypropionate) oligomer (P3HP) was <NUM>,<NUM>/mol.

In a <NUM> round flask, <NUM> parts by weight of L-lactide, <NUM> parts by weight of the poly(<NUM>-hydroxypropionate) oligomer prepared in (<NUM>), and <NUM> mol% (with respect to <NUM>% by weight of L-lactide) of tin(II) <NUM>-ethylhexanoate were put and vacuum-dried at room temperature for <NUM> hours by sufficiently applying a vacuum.

Thereafter, the flask was placed in an oil bath pre-heated at <NUM>, the temperature of which was raised to <NUM>, and then a ring-opening polymerization reaction was carried out for <NUM> minutes to <NUM> minutes. After the reaction was completed, the reaction product was dissolved in chloroform and then extracted with methanol to recover a P(LLA-b-3HP) copolymer having a weight average molecular weight of <NUM>,<NUM>/mol.

A P(LLA-b-3HP) copolymer having a weight average molecular weight of <NUM>,<NUM>/mol was prepared in the same manner as in Preparation Example <NUM>-<NUM>, except that <NUM> parts by weight of L-lactide, <NUM> parts by weight of poly(<NUM>-hydroxypropionate) oligomer, and <NUM> mol% (with respect to <NUM>% by weight of L-lactide) of tin(II) <NUM>-ethylhexanoate were used in (<NUM>) of Preparation Example <NUM>-<NUM>.

A weight average molecular weight of the prepared poly(<NUM>-hydroxypropionate) oligomer was <NUM>,<NUM>/mol.

Thereafter, the flask was placed in an oil bath pre-heated at <NUM>, the temperature of which was raised to <NUM>, and then a ring-opening polymerization reaction was carried out for <NUM> minutes. After the reaction was completed, the reaction product was dissolved in chloroform and then extracted with methanol to recover a P(LLA-b-3HP) copolymer having a weight average molecular weight of <NUM>,<NUM>/mol.

In a <NUM> round flask, <NUM> of L-lactide, and <NUM>µl (<NUM> mol% with respect to <NUM>% by weight of L-lactide) of tin(II) <NUM>-ethylhexanoate were put and vacuum-dried at room temperature (<NUM>) for <NUM> hours by sufficiently applying a vacuum.

Thereafter, the flask was placed in an oil bath pre-heated at <NUM>, the temperature of which was raised to <NUM>, and then a ring-opening polymerization reaction was carried out for <NUM> minutes. After the reaction was completed, the reaction product was dissolved in chloroform and then extracted with methanol to recover a PLLA polymer having a weight average molecular weight of <NUM>,<NUM>/mol.

In a <NUM> round flask, <NUM> of D-lactic acid and <NUM> of p-toluenesufonic acid catalyst were put and allowed to react under conditions of <NUM> mbar and <NUM> for <NUM> hours and under conditions of <NUM> mbar and <NUM> for <NUM> hours to obtain a PDLA polymer having a weight average molecular weight of <NUM>,<NUM>/mol.

In a <NUM> round flask, <NUM> (<NUM> mmol) of D-lactide, <NUM> (<NUM> mmol) of <NUM>-octanol, and <NUM> mol% (with respect to <NUM>% by weight of D-lactide) of tin(II) <NUM>-ethylhexanoate were put and vacuum-dried at room temperature for <NUM> hours by sufficiently applying a vacuum.

Thereafter, the flask was placed in an oil bath pre-heated at <NUM>, the temperature of which was raised to <NUM>, and then a ring-opening polymerization reaction was carried out for <NUM> minutes. After the reaction was completed, the reaction product was dissolved in chloroform and then extracted with methanol to recover a PDLA polymer having a weight average molecular weight of <NUM>,<NUM>/mol.

<NUM> parts by weight of the P(LLA-b-3HP) copolymer prepared in Preparation Example <NUM>-<NUM> and <NUM> parts by weight of the PDLA polymer prepared in Preparation Example <NUM>-<NUM> were put in a stirring reactor, and stirred at atmospheric pressure (<NUM> Torr) at <NUM> for <NUM> minutes to prepare a polylactate stereocomplex.

Each polylactate stereocomplex was prepared in the same manner as in Example <NUM>, except that substances described in Table <NUM> below were used as P(LLA-b-3HP) (or PLLA) and PDLA, and the content of PDLA was controlled as described in Table <NUM> below.

A commercially available PLLA polymer, Ingeo™ Biopolymer 2003D (PLA <NUM> D) produced by Nature Works, was used as Comparative Example <NUM>.

Physical properties were evaluated for the polymers prepared in Preparation Examples and the polylactate stereocomplexes of Examples and Comparative Examples by the following methods, and the results are shown in Tables <NUM> and <NUM>.

A weight average molecular weight (Mw) and a number average molecular weight (Mn) of each polymer were determined by gel permeation chromatography (GPC) (Waters: Waters707). A polydispersity index (PDI) was calculated by dividing the measured weight average molecular weight by the number average molecular weight.

The polymer to be measured was dissolved in chloroform to a concentration of <NUM> ppm, and <NUM>µl thereof was injected into GPC. Chloroform was used as a mobile phase of GPC, a flow rate was <NUM>/min, and analysis was performed at <NUM>. As a column, four Waters HR-<NUM>,<NUM>,<NUM>,4E were connected in series. RI and PAD detectors were used as detectors, and the measurement was performed at <NUM>.

A melting enthalpy and a melting temperature were measured using a differential scanning calorimeter (DSC, manufacturer: Mettler Toledo) by the following method.

The polymer (or stereocomplex) was heated to <NUM>, and then maintained for <NUM> minutes, and the temperature was decreased to -<NUM> to remove thermal history, and then heated to <NUM> and the melting temperature (Tm) and the melting enthalpy (ΔH) were measured from a peak of the secondary heating. At this time, the heating and cooling rates were controlled to <NUM>/min, respectively.

Elongation was measured for the stereocomplexes of Examples <NUM> to <NUM> and Comparative Example <NUM>, and the P(LLA-b-3HP) copolymer of Preparation Example <NUM>-<NUM> by the following method.

Each dogbone-shaped test specimen corresponding to ASTM D638 Type V was prepared at <NUM> using a hot-press (Limotem QM900S) device.

The elongation was measured for the prepared specimen according to a measurement method of IPC-TM-<NUM> using a tensile strength meter (manufacturer: Instron, model name: <NUM> UTM).

Referring to Table <NUM>, it was confirmed that the stereocomplexes of Examples <NUM> to <NUM> exhibited remarkably improved heat resistance property, as compared with the P(LLA-b-3HP) copolymer alone or the commercially available polylactate resin, and had remarkably improved tensile elongation, as compared with the stereocomplex of Comparative Example <NUM> prepared from poly(L-lactate) and poly(D-lactate).

Meanwhile, Comparative Example <NUM>, in which P(LLA-b-3HP) including more than <NUM> parts by weight of the poly(<NUM>-hydroxypropionate) repeating unit was used, exhibited the melting temperature of lower than <NUM>, indicating that the complex was not formed. Further, Comparative Example <NUM>, in which PDLA having a weight average molecular weight of more than <NUM>,<NUM>/mol was used, showed formation of the stereocomplex, but its tensile elongation characteristic was remarkably reduced, as compared with those of Examples <NUM> to <NUM>.

Claim 1:
A polylactate stereocomplex, comprising:
a poly(L-lactate-<NUM>-hydroxypropionate) block copolymer including <NUM> parts by weight to <NUM> parts by weight of a poly(<NUM>-hydroxypropionate) repeating unit with respect to <NUM> parts by weight of a poly(L-lactate) repeating unit; and
a poly(D-lactate) having a weight average molecular weight of <NUM>,<NUM>/mol or more to less than <NUM>,<NUM>/mol, wherein the weight average molecular weight is measured by gel permeation chromatography as disclosed in the specification.