Patent Description:
Polyhydroxyalkanoate is a type of linear polyester synthesized by bacteria as a source of energy stored in the cells in a growth environment with nutrient deficiency conditions, e.g., excess supply of carbon sources, lack of nitrogen, phosphorus, oxygen, etc. Polyhydroxyalkanoate has physical and chemical properties similar to those of petrochemical-based plastics, and also possesses biocompatibility characteristic which is not found in petrochemical-based plastics. However, in comparison to petrochemical-based plastics which are difficult to be degraded, polyhydroxyalkanoate can be completely degraded into carbon dioxide and water by microorganisms in a natural environment, and thus, is expected to replace petrochemical-based plastics.

The physical properties of polyhydroxyalkanoate are mainly affected by the type, content and arrangement of monomer units thereof. On the other hand, the chemical structure of polyhydroxyalkanoate is very diverse, and might be affected by the type of bacteria, the type of medium, and/or the type of carbon source involved in synthesizing the polyhydroxyalkanoate. At present, there are more than <NUM> types of different monomer units that make up polyhydroxyalkanoates. Examples of commonly known polyhydroxyalkanoate include, among others, poly-<NUM>-hydroxybutyrate (PHB), poly-<NUM>-hydroxyvalerate (PHV), and poly(<NUM>-hydroxybutyrate-co-<NUM>-hydroxyvalerate) (PHBV) which is a random copolymer formed from <NUM>-hydroxybutanoic acid and <NUM>-hydroxyvaleric acid.

<CIT>, paragraph [<NUM>], relates to a co-culture system comprising two different strains of the bacterium Ralstonia eutropha (Cupriavidus necator) and its use for production of value-added compounds. Paragraph [<NUM>] specifies that if levulinic acid (<NUM>-ketovaleric acid) is present in the feedstock, the co-culture system disclosed herein may use it for production of poly(<NUM>-hydroxybutyrate-co-<NUM>-hydroxyvalerate) (PHBV) and/or poly(<NUM>-hydroxybutyrate-co-<NUM>-hydroxyvalerate-co-<NUM>-hydroxyvalerate) (P(3HB-co-3HV-co-4HV). Paragraphs [<NUM>], [<NUM>], [<NUM>], [<NUM>], [<NUM>] and [<NUM>] disclose a poly(<NUM>-hydroxybutyrate-co-<NUM>-hydroxyvalerate-co-<NUM>-hydroxyvalerate) (PHBVV, P(3HB-co-3HV-co-4HV)).

The applicants, in an article entitled "<NPL>, discloses a polyhydroxyalkanoate copolymer which includes monomeric units that are randomly arranged and which has a good mechanical property. In order to further improve the properties of the polyhydroxyalkanoate copolymer, the applicants has endeavor to develop another polyhydroxyalkanoate copolymer having a molecular structure different from that of the aforesaid polyhydroxyalkanoate copolymer.

Therefore, in a first aspect, the present disclosure provides a polyhydroxyalkanoate block copolymer which can alleviate at least one of the drawbacks of the prior art.

The polyhydroxyalkanoate block copolymer includes a first segment containing a first monomeric unit represented by formula (I), and a second segment containing the first monomeric unit represented by formula (I), a second monomeric unit represented by formula (II), and a third monomeric unit represented by formula (III),
<CHM>
<CHM>
The first segment and the second segment are arranged in blocks.

In a second aspect, the present disclosure provides a method for preparing a polyhydroxyalkanoate block copolymer, which can alleviate at least one of the drawbacks of the prior art.

In step (a) of the method, the gluconic acid is completely consumed by Cupriavidus necator H16, so that a first segment containing a first monomeric unit represented by formula (I) is generated in Cupriavidus necator H16, and the fermented culture is substantially free of the gluconic acid. The first segment and the second segment are arranged in blocks. The second segment contains the first monomeric unit represented by formula (I), a second monomeric unit represented by formula (II), and a third monomeric unit represented by formula (III),
<CHM>
<CHM>.

Other features and advantages of the present disclosure will become apparent in the following detailed description of the embodiment(s) with reference to the accompanying drawings. It is noted that various features may not be drawn to scale.

Before the present disclosure is described in greater detail, it should be noted that if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Taiwan or any other country.

For the purpose of this specification, it will be clearly understood that the word "comprising" means "including but not limited to", and that the word "comprises" has a corresponding meaning.

Unless otherwise defined, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which the present disclosure belongs. One skilled in the art will recognize many methods and materials similar or equivalent to those described herein, which could be used in the practice of the present disclosure. Indeed, the present disclosure is in no way limited to the methods and materials described.

The present disclosure provides a polyhydroxyalkanoate block copolymer which includes a first segment containing a first monomeric unit represented by formula (I), and a second segment containing the first monomeric unit represented by formula (I), a second monomeric unit represented by formula (II), and a third monomeric unit represented by formula (III),
<CHM>
<CHM>
The first segment and the second segment are arranged in blocks.

In certain embodiments, the first monomeric unit, the second monomeric unit, and the third monomeric unit are randomly arranged in the second segment.

According to the present disclosure, based on the total amount of the first segment and the second segment as <NUM> mol%, the second monomeric unit is present in an amount ranging from <NUM> mol% to <NUM> mol%, the third monomeric unit is present in an amount ranging from <NUM> mol% to <NUM> mol%, and a balance is an amount of the first monomeric unit, such that the polyhydroxyalkanoate block copolymer has an improved mechanical property.

The present disclosure also provides a method for preparing the polyhydroxyalkanoate block copolymer which includes the following steps (a) and (b).

In step (a), Cupriavidus necator H16 is cultivated in a liquid medium containing gluconic acid as a first carbon source, followed by conducting a first fermentation process to obtain a fermented culture. The gluconic acid is completely consumed by Cupriavidus necator H16, so that a first segment containing a first monomeric unit represented by the formula (I),
<CHM>
is generated in Cupriavidus necator H16, and the fermented culture is substantially free of the gluconic acid.

In step (b), levulinic acid is added as a second carbon source into the fermented culture, followed by conducting a second fermentation process, so that the levulinic acid is consumed by Cupriavidus necator H16, followed by generation of a polyhydroxyalkanoate block copolymer including the first segment and the second segment in Cupriavidus necator H16. The second segment contains the first monomeric unit represented by the aforesaid formula (I), the second monomeric unit represented by formula (II), and a third monomeric unit represented by formula (III),
<CHM>
The first segment and the second segment are arranged in blocks.

According to the present disclosure, Cupriavidus necator H16 (also known as Ralstonia eutropha H16) is a known bacterial strain that is readily available to the public, and may be purchased from the American Type Culture Collection under an accession number ATCC <NUM>, German Collection of Microorganisms and Cell Cultures GmbH under an accession number DSM <NUM>, or the Bioresource Collection and Research Center (BCRC) of the Food Industry Research and Development Institute (FIRDI), Taiwan, under an accession number BCRC <NUM>.

In certain embodiments, in step (a), instead of the liquid medium containing gluconic acid, Cupriavidus necator H16 may be cultivated in the liquid medium containing levulinic acid as the first carbon source, followed by conducting the first fermentation process to obtain the fermented culture. That is, in step (a), the levulinic acid is completely consumed by Cupriavidus necator H16, so that the second segment containing the first monomeric unit represented by the aforesaid formula (I), the second monomeric unit represented by the aforesaid formula (II), and the third monomeric unit represented by the aforesaid formula (III), is generated in Cupriavidus necator H16, and the fermented culture is substantially free of the levulinic acid. Afterwards, in step (b), gluconic acid is added as the second carbon source into the fermented culture, followed by conducting the second fermentation process, so that the gluconic acid is consumed by Cupriavidus necator H16, followed by generation of the polyhydroxyalkanoate block copolymer including the second segment and the first segment containing the first monomeric unit represented by the aforesaid formula (I) in Cupriavidus necator H16, and the fermented culture is substantially free of the gluconic acid. The first segment and the second segment are arranged in blocks.

According to the present disclosure, in order to allow the first segment and the second segment of the polyhydroxyalkanoate block copolymer to be arranged in blocks, in step (a), when gluconic acid is used as the first carbon source for cultivating Cupriavidus necator H16 so as to obtain the fermented culture, step (b) of adding the levulinic acid as the second carbon source into the fermented culture is conducted only after the fermented culture is substantially free of the gluconic acid. In other words, in step (a), if the gluconic acid is not completely consumed by Cupriavidus necator H16, step (b), i.e., adding the levulinic acid into the fermented culture, will not be conducted. Likewise, in certain embodiments, in step (a), when levulinic acid is used as the first carbon source for cultivating Cupriavidus necator H16 so as to obtain the fermented culture, step (b) of adding the gluconic acid as the second carbon source into the fermented culture is conducted only after the fermented culture is substantially free of the levulinic acid. In other words, in step (a), if the levulinic acid is not completely consumed by Cupriavidus necator H16, step (b), i.e., adding the gluconic acid into the fermented culture, will not be conducted.

According to the present disclosure, in an exemplary embodiment, in step (a), gluconic acid is used as the first carbon source, and in step (b), the levulinic acid is used as the second carbon source, so that the growth rate of Cupriavidus necator H16 can be increased, thereby improving the yield of the polyhydroxyalkanoate block copolymer.

According to the present disclosure, the polyhydroxyalkanoate block copolymer may be obtained when steps (a) and (b) of the method are conducted once. It should be noted that, in order to increase the numbers of the first segment and the second segment of the polyhydroxyalkanoate block copolymer, each of steps (a) and (b) is repeatedly conducted a plurality of times. In addition, the longer the time period for conducting steps (a) and (b), the longer the lengths of the first segment and the second segment of the polyhydroxyalkanoate block copolymer are. In certain embodiments, each of steps (a) and (b) is repeatedly conducted a plurality of times.

According to the present disclosure, the amount of the first monomeric unit may be regulated by controlling the concentration of the gluconic acid, and the amount of the second monomeric unit may be regulated by controlling the concentration of the levulinic acid. In certain embodiments, in order to confer improved mechanical properties to the polyhydroxyalkanoate block copolymer, in step (a), the liquid medium contains <NUM>% w/v to <NUM>% w/v of the gluconic acid. In certain embodiments, in order to confer improved mechanical properties to the polyhydroxyalkanoate block copolymer, in step (b), the fermented culture contains <NUM>% w/v to <NUM>% w/v of the levulinic acid.

In certain embodiments, the liquid medium is a mineral salt liquid medium. The composition of the mineral salt liquid medium is not particularly limited, as long as the mineral salt liquid medium is suitable for the growth of Cupriavidus necator H16, and can be flexibly adjusted by those skilled in the art according to growth requirements of Cupriavidus necator H16. In certain embodiments, the mineral salt liquid medium which includes water, Na<NUM>HPO<NUM>·<NUM><NUM>O, KH<NUM>PO<NUM>, (NH<NUM>)<NUM>SO<NUM> and MgSO<NUM>·<NUM><NUM>O.

The present disclosure will be described by way of the following examples. However, it should be understood that the following examples are intended solely for the purpose of illustration and should not be construed as limiting the present disclosure in practice.

First, Cupriavidus necator H16 (purchased from Bioresource Collection and Research Center (BCRC) of the Food Industry Research and Development Institute (FIRDI), Taiwan, under an accession number BCRC <NUM>) was inoculated into <NUM> of an LB broth (Manufacturer: BD Difco™), and was then cultured at a temperature of <NUM> for a time period ranging from <NUM> hours to <NUM> hours to activate the bacterial strain, thereby obtaining a bacterial culture. At the same time, a mineral salt liquid medium was prepared, and includes water, Na<NUM>HPO<NUM>·<NUM><NUM>O having a concentration of <NUM>/L, KH<NUM>PO<NUM> having a concentration of <NUM>/L, (NH<NUM>)<NUM>SO<NUM> having a concentration of <NUM>/L, MgSO<NUM>·<NUM><NUM>O having a concentration of <NUM>/L, CaCl<NUM>·<NUM><NUM>O having a concentration of <NUM>/L, FeSO<NUM>·<NUM><NUM>O having a concentration of <NUM>/L, and a trace element solution having a concentration of <NUM>/L. The trace element solution includes H<NUM>BO<NUM> having a concentration of <NUM>/L, CoCl<NUM> ·<NUM><NUM>O having a concentration of <NUM>/L, ZnSO4 ·<NUM><NUM>O having a concentration of <NUM>/L, MnCl<NUM> ·<NUM><NUM>O having a concentration of <NUM>/L, Na<NUM>MoO<NUM> ·<NUM><NUM>O having a concentration of <NUM>/ L, NiCl<NUM> ·<NUM><NUM>O having a concentration of <NUM>/L, and CuSO<NUM> ·<NUM><NUM>O having a concentration of <NUM>/L.

Next, <NUM> of the bacterial culture was cultivated in <NUM> of the mineral salt liquid medium containing <NUM>% w/v of gluconic acid, so as to conduct first fermentation process at a temperature of <NUM> and under a speed of <NUM> rpm for a predetermined time period, thereby obtaining a first fermented culture. During the first fermentation process, the bacterial culture was subjected to light absorbance measurements at a wavelength of <NUM> (OD<NUM>) using a spectrophotometer (Manufacturer: Hitachi, Ltd. ; Model no. : U-<NUM>) so as to determine growth condition of Cupriavidus necator H16, until the bacterial count no longer increased, indicating that the gluconic acid had been completely consumed by Cupriavidus necator H16. Thereafter, levulinic acid was added to the fermented culture such that the fermented culture contained <NUM>% w/v of levulinic acid, followed by conducting a second fermentation process at a temperature of <NUM> and under a speed of <NUM> rpm for a predetermined time period, thereby obtaining a second fermented culture. During the second fermentation process, the fermented culture was subjected to light absorbance measurements at a wavelength of <NUM> (OD<NUM>) using the aforesaid spectrophotometer so as to determine growth condition of Cupriavidus necator H16, until the bacterial count no longer increased, indicating that the levulinic acid had been completely consumed by Cupriavidus necator H16. Then, the first fermentation process utilizing gluconic acid as the single carbon source and the second fermentation process utilizing levulinic acid as the single carbon source were sequentially and repeatedly conducted (i.e., the gluconic acid and the levulinic acid did not coexist in the first and second fermented cultures) for a total time period of <NUM> hours, thereby obtaining a final fermented culture.

Thereafter, the final fermented culture was subjected to centrifugation under a speed of <NUM> ×g for <NUM> minutes so as to form supernatant and pellet fractions. After the supernatant was removed, the pellet was subjected to a freeze-drying treatment, so as to obtain a dried bacterial powder. Then, <NUM> of the dried bacterial powder was added into <NUM> of dichloromethane, followed by heating at <NUM> for <NUM> hours so as to obtain a crude extract. Afterwards, the crude extract was left to stand so as to allow cell debris to settle, followed by subjecting the crude extract to a filtration process using a filter paper (Manufacturer: Advantec Co. ), so as to collect the filtrate. Subsequently, the filtrate was slowly dropped onto ice-cold methanol having a volume <NUM> times of that of the filtrate under continuous stirring, so as to precipitate polyhydroxyalkanoate block copolymer therefrom, thereby obtaining a polyhydroxyalkanoate block copolymer of EX1. The polyhydroxyalkanoate block copolymer of EX1 was washed once with <NUM>% methanol, and then placed in a vacuum suction apparatus for removal of residual organic solvent, until a constant weight was achieved.

The procedures and conditions for preparing the polyhydroxyalkanoate block copolymer of EX2 were substantially similar to those of EX1, except that in EX2, the fermented culture contained <NUM>% w/v of levulinic acid.

A respective one of the polyhydroxyalkanoate block copolymers of EX1 and EX2 was dissolved in deuterated chloroform, and then subjected to NMR spectroscopy using an NMR spectrometer (Manufacturer: JEOL, Ltd. ; Model no. : ECZ-600R). The results are shown in <FIG>. To be specific, for the polyhydroxyalkanoate block copolymer of EX1, the <NUM>H-NMR spectra thereof are respectively shown in <FIG> and <FIG>, while the <NUM>C-NMR spectra thereof are respectively shown in <FIG> and <FIG>. For the polyhydroxyalkanoate block copolymer of EX2, the <NUM>H-NMR spectra thereof are respectively shown in <FIG> and <FIG>, while the <NUM>C-NMR spectra thereof are respectively shown in <FIG> and <FIG>.

The identities of the peaks at specific chemical shift ranges in the <NUM>H-NMR spectra of the polyhydroxyalkanoate block copolymers of EX1 and EX2 were determined based on to an article by<NPL>. Referring to <FIG>, <FIG>, <FIG> and <FIG>, in the <NUM>H-NMR spectra of the polyhydroxyalkanoate block copolymers of EX1 and EX2, the chemical shift signal at between <NUM> ppm to <NUM> ppm was indicative of the presence of the first monomeric unit represented by formula (I) (abbreviated as 3HB), the chemical shift signal at between <NUM> ppm to <NUM> ppm was indicative of the presence of the second monomeric unit represented by formula (II) (abbreviated as 3HV), and the chemical shift signal at between <NUM> ppm to <NUM> ppm was indicative of the presence of the third monomeric unit represented by formula (III) (abbreviated as 4HV). Referring again to the <NUM>H-NMR spectra of the polyhydroxyalkanoate block copolymers of EX1 shown in <FIG>, a ratio of the integrated peak area at chemical shift region of the first monomeric unit to the integrated peak area at chemical shift region of the second monomeric unit to the integrated peak area at chemical shift region of the third monomeric unit is determined, so as to calculate the amounts (in mol%) of the first monomeric unit, the second monomeric unit, and the third monomeric unit of the polyhydroxyalkanoate block copolymers of EX1. Likewise, the amounts (in mol%) of the first monomeric unit, the second monomeric unit and the third monomeric unit of the polyhydroxyalkanoate block copolymers of EX2 can be calculated after determining the ratio of the integrated peak area at chemical shift region of the first monomeric unit to the integrated peak area at chemical shift region of the second monomeric unit to the integrated peak area at chemical shift region of the third monomeric unit.

Referring to the <NUM>C-NMR spectra of the polyhydroxyalkanoate block copolymers of EX1 and EX2 respectively shown in <FIG> and <FIG>, after determining the integrated peak areas at chemical shift regions of <NUM> ppm to <NUM> ppm, the D values of the polyhydroxyalkanoate block copolymers of EX1 and EX2 were respectively calculated using the following Equation (I): <MAT> in which.

The polyhydroxyalkanoate block copolymer of EX2 was further subjected to DSC analysis with using a differential scanning calorimeter (DSC) (Manufacturer: TA Instruments, Inc. ; Model: DSC Q100). The DSC analysis includes a first heating treatment, in which the test temperature was raised from - <NUM> to <NUM> at a heating rate of <NUM>/minute and then kept at <NUM> for <NUM> minutes, and a second heating treatment, in which the test temperature was raised from -<NUM> to <NUM> at a heating rate of <NUM>/minute. The DSC curve of the first heating treatment is shown in <FIG>, and the DSC curve of the second heating treatment is shown in <FIG>. The first and second melting temperatures determined from the first heating treatment, and the crystallization temperature and the glass transition temperature determined from the second heating treatment are shown in Table <NUM>.

<NPL>, and <NPL>, disclose that if a polyhydroxyalkanoate copolymer has a D value greater than <NUM>, such polyhydroxyalkanoate copolymer has a block structure. Referring to Table <NUM>, the polyhydroxyalkanoate block copolymers of EX1 and EX2 each has a block structure because the D value thereof is greater than <NUM>.

<NPL>, discloses that the melting temperature of a random copolymer consisting of <NUM> mol% of 3HV and <NUM> mol% of 3HB is <NUM>, and the melting temperature of a homopolymer consisting of <NUM> mol% of 3HB is <NUM>. Referring to Tables <NUM> and <NUM> and <FIG>, the contents of 3HV and 3HB in the polyhydroxyalkanoate block copolymer of EX2 are substantially similar to those of the random copolymer disclosed in the aforesaid article, however, the polyhydroxyalkanoate block copolymer of EX2 has a first melting temperature, Tm1 (i.e., <NUM>), and a second melting temperature, Tm2 (i.e., <NUM>), that are completely different from the melting temperature of the random copolymer disclosed in the aforesaid article, indicating that the polyhydroxyalkanoate block copolymer of EX2 should be a polyhydroxyalkanoate block copolymer including two different segments, and the monomeric units of these two segments are different from each other. Since the second melting temperature, Tm2 (i.e., <NUM>), of the polyhydroxyalkanoate block copolymer of EX2 is approximately similar to the melting temperature (i.e., <NUM>) of the homopolymer consisting of <NUM> mol% of 3HB as disclosed in the aforesaid article, one of the two segments of the polyhydroxyalkanoate block copolymer of EX2 is entirely consists of 3HB, and thus, the first melting temperature, Tm1 (i.e., <NUM>) of the polyhydroxyalkanoate block copolymer of EX2 should be contributed by the presence of the other one of the two segments which consists of randomly arranged 3HV, 3HB and 4HV. In addition, referring again to <FIG>, the peak area of the second melting temperature, Tm2, is significantly greater than the peak area of the first melting temperature, Tm1, suggesting that, in the polyhydroxyalkanoate block copolymer of EX2, the segment entirely consisting of 3HB serves as the main polymer block whereas the other segment consisting of randomly arranged 3HV, 3HB and 4HV serves as the secondary polymer block.

<NPL>, discloses that a homopolymer consisting of 3HB has a glass transition temperature ranging from -<NUM> to -<NUM>, and a crystallization temperature ranging from <NUM> to <NUM>. Referring to Table <NUM> and <FIG>, the glass transition temperature, Tg (i.e., <NUM>) of the polyhydroxyalkanoate block copolymer of EX2 is within the glass transition temperature range of the homopolymer consisting of 3B disclosed in the aforesaid article, however, the polyhydroxyalkanoate block copolymer of EX2 has a crystallization temperature, Tc (i.e., <NUM>) that is significantly different from that of the homopolymer consisting of 3B disclosed in the aforesaid article, indicating that in the polyhydroxyalkanoate block copolymer of EX2, the segment consisting of 3HB and the other segment consisting of randomly arranged 3HV, 3HB and 4HV exist to form a block copolymer chain, and are not blended to each other.

<NPL>, discloses that the crystallization temperature of a polymer, e.g., a homopolymer consisting of 3HB, can be readily determined from a DSC curve obtained by DSC analysis, however, the crystallinity of a random copolymer consisting of 3HV and 3HB correspondingly decreased with increase of 3HB content therein, resulting in the peak representing the crystallization temperature of the random polymer becoming less obvious, and when 3HB was present in an amount of up to <NUM> mol%, the peak representing the crystallization temperature of such random polymer became significantly less obvious, which results in the crystallization temperature of such random polymer cannot be readily determined from the DSC curve. However, as shown in <FIG>, the DSC curve of the polyhydroxyalkanoate block copolymer of EX2 has a very significant peak which allows the crystallization temperature, Tc (i.e., <NUM>), to be readily determined, indicating that the polyhydroxyalkanoate block copolymer of EX2 has a block structure, and monomeric units thereof are not randomly arranged.

The aforesaid results and discussions confirm that the polyhydroxyalkanoate block copolymers of EX1 and EX2 includes a first segment which contains 3HB and which serves as a main polymer block, and a second segment which contains the randomly arranged 3HV, 3HB and 4HV and which serves as a secondary polymer block. The first segment and the second segment are arranged in blocks.

The applicants, in an article entitled "<NPL>, discloses that a low content of 4HV allows the resultant polyhydroxyalkanoate copolymer to have good ductility. Referring back to Table <NUM>, since 4HV is present in an amount ranging from <NUM> mol% to <NUM> mol% in each of the polyhydroxyalkanoate block copolymers of EX1 and EX2, the polyhydroxyalkanoate block copolymers of EX1 and EX2 are expected to have good ductility.

In addition, <NPL>, and <NPL>, disclose that with regard to polyhydroxyalkanoates, in comparison to random copolymers, block copolymers have improved anti-aging properties and would not become brittle for a long period of storage. Since the aforesaid results and discussions demonstrated that the polyhydroxyalkanoate block copolymers of EX1 and EX2 indeed have block structures, the polyhydroxyalkanoate block copolymers of EX1 and EX2 are expected to have good anti-aging properties.

In summary, in the method for preparing the polyhydroxyalkanoate block copolymer of the present disclosure, by cultivating Cupriavidus necator H16 in the liquid medium containing gluconic acid and then conducting the first fermentation process to obtain the fermented culture that is substantially free of gluconic acid, followed by adding levulinic acid to the fermented culture and then conducting a second fermentation process so that the levulinic acid is consumed by Cupriavidus necator H16, the polyhydroxyalkanoate block copolymer including the first segment and the segment that are arranged in blocks are generated, and such polyhydroxyalkanoate block copolymer has good anti-aging properties.

Claim 1:
A polyhydroxyalkanoate block copolymer, characterized by:
a first segment containing a first monomeric unit represented by formula (I); and
a second segment containing the first monomeric unit represented by formula (I), a second monomeric unit represented by formula (II), and a third monomeric unit represented by formula (III),
<CHM>
<CHM>
<CHM>
wherein the first segment and the second segment are arranged in blocks.