Method for synthesizing polyhydroxy acid ester through oxidation of alcohol and air and product

Abstract

The invention discloses a method for synthesizing polyhydroxy acid ester through oxidation of alcohol and air, which comprises the following steps: S1, in an aerobic atmosphere, monohydric alcohol and / or dihydric alcohol are / is oxidized and react with alkali to form hydroxy acid salt; s2, mixing and neutralizing hydroxy acid salt and acid to form hydroxy acid, and then dehydrating to obtain an intermediate product; s3, polymerizing the intermediate product prepared in the step S2 under the action of a metal alkaline catalyst and a hydroxyl compound initiator to prepare polyhydroxy acid ester; wherein the metal basic catalyst comprises one or more of metal alkoxides and / or organic acid salt compounds of tin, titanium, zinc, aluminum, potassium, sodium, lithium, copper, iron and antimony, and the hydroxyl compound comprises alcohols and / or water. The biodegradable polyhydroxy acid ester plastic can be prepared by directly utilizing low-cost monohydric alcohol or dihydric alcohol as a raw material, the production process is simple, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material synthesis, and particularly relates to a method and product for synthesizing polyhydroxy esters by oxidizing alcohol and air. The method synthesizes polyhydroxy esters by oxidizing monohydric alcohol or dihydric alcohol with air. Background Art

[0002] Non-degradable plastics such as polyolefins have led to increasingly serious global white pollution, seriously affecting the ecological environment. It has become a general consensus to use biodegradable plastics with complete degradation functions to replace traditional non-degradable plastics.

[0003] At present, the main category of biodegradable plastics is polyesters whose repeating units in the main molecular chain are connected by ester bonds. Among them, polyhydroxy ester is a type of aliphatic polyester, which has the characteristics of high thermal stability, biocompatibility, biodegradability and solvent resistance. It is similar to the basic physical properties of petrochemical synthetic plastics, has good gloss and transparency, and is similar to film products made of polystyrene, making it suitable as a raw material for biodegradable plastics.

[0004] However, the synthesis of existing polyhydroxy esters is usually based on biofermentation, which is difficult to scale up. As a result, the price of polyhydroxy ester products is several times higher than that of ordinary polyolefin plastics, which greatly hinders their commercial application. For example, synthetic polylactic acid (PL) is prepared from food resources such as corn. Specifically, corn is saccharified to obtain glucose, which is then fermented and purified by bacteria to produce high-purity lactic acid, which is then converted into the intermediate monomer lactide, ultimately achieving the synthesis of PLA. As another example, polyhydroxyalkyl esters (PHAs) are usually obtained by fermenting and converting crop-derived sugars or specific carbon source substrates through genetically engineered bacteria, and then extracting them from the inside of the cells using organic solvents.

[0005] CN111194353A discloses a poly (3-hydroxypropionate-B-lactate) block copolymer prepared using microorganisms, which utilizes modified recombinant Escherichia coli, glycerol derived from crops such as soybeans as a carbon source, and biosynthesizes P (3HP) in the early stages of culture through 3-hydroxypropionate production genes and enhanced PHA synthase. CN118516416A, a PHA-producing engineered halomonas and a PHA production method, by reducing the expression level of the cytochrome d oxidase complex gene cydA or the activity of its encoded protein, efficiently synthesizes PHA using glucose derived from crops such as corn as a carbon source, effectively increasing the yield of PHA. CN118291557A, a coenzyme A transferase and its screening method and its application in the synthesis of P34HB, using glucose derived from crops such as corn as a carbon source, by constructing recombinant vectors of coenzyme A transferases from different sources, successfully introducing them into halomonas, and detecting the yield of the copolymer P34HB by fermentation.

[0006] In summary, the raw materials for the synthesis of polyhydroxy esters (PHEs) are generally food crops like corn and soybeans, which compete with human rations and animal feed. Furthermore, the products of natural bacterial metabolism of carbohydrates are complex, requiring the use of genetically engineered strains like Escherichia coli to produce a relatively simple product, which is costly, and subsequent purification requires even more expense. Therefore, existing biofermentation methods are prohibitively expensive, and actual production capacity is far from meeting the demand for PHEs.

[0007] Based on this, the present invention proposes a low-cost and efficient method for synthesizing polyhydroxy esters, which does not require biological fermentation but directly utilizes low-cost non-grain-based raw materials to prepare polyhydroxy esters. Summary of the Invention

[0008] To solve the above technical problems, the purpose of the present invention is to provide a method and product for synthesizing polyhydroxy esters by oxidizing alcohols and air. The method can directly use low-cost monohydric or dihydric alcohols as raw materials to prepare biodegradable polyhydroxy ester plastics, simplify the production process, and reduce production costs.

[0009] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0010] In the first aspect of the present invention, the present invention provides a method for synthesizing polyhydroxy esters by oxidation using alcohol and air, as follows:

[0011] S1. In an oxygen atmosphere, a monohydric alcohol and / or a dihydric alcohol is oxidized and reacts with a base to form a hydroxy acid salt;

[0012] S2, neutralizing the hydroxy acid salt obtained in step S1 with an acid to form a hydroxy acid, and then dehydrating the hydroxy acid to obtain an intermediate product;

[0013] S3, polymerizing the intermediate product obtained in step S2 under the action of a metal alkaline catalyst and a hydroxy compound initiator to obtain a polyhydroxy acid ester;

[0014] Among them, diols include:

[0015]

[0016]

[0017] and / or,

[0018]

[0019] Monohydric alcohols include:

[0020]

[0021] The metal alkaline catalyst includes one or more metal alkoxides and / or organic acid salt compounds of tin, titanium, zinc, aluminum, potassium, sodium, lithium, copper, iron, and antimony, and the hydroxyl compound includes alcohols and / or water.

[0022] Preferably, in step S1, under the action of a synergistic catalyst, the monohydric alcohol and / or dihydric alcohol is oxidized and reacts with a base to form a hydroxy acid salt;

[0023] Among them, the synergistic catalyst includes a main catalyst and a co-catalyst, the metal elements in the main catalyst include Group VIII transition metals, copper subgroup metals, zinc subgroup metals, and Group IIIA-VIA metals, and the co-catalyst includes phosphine and / or nitrogen-based ligands.

[0024] More preferably, the main catalyst comprises one or more of metal halides, acetates, sulfates and nitrates of ruthenium, rhodium, palladium, iron, cobalt, nickel, copper, zinc and gold, and the co-catalyst comprises one or more of triphenylphosphine, triphenylphosphine oxide, tri-tert-butylphosphine, tricyclohexylphosphine, bis(2-diphenylphosphine)phenyl ether, 2,2,6,6-tetramethylpiperidinyl oxide, 2,2'-bipyridine, ethylenediamine and o-phenanthroline;

[0025] More preferably, the main catalyst includes one or more of ruthenium trichloride, rhodium acetate, ferric chloride, cobalt trichloride, rhodium trichloride, gold trichloride, palladium chloride, copper chloride and zinc chloride.

[0026] Preferably, in step S1, the base includes one or more of hydroxides, carbonates and nitrogen-containing compounds, more preferably, the base includes one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate and tetramethylammonium hydroxide.

[0027] Preferably, in step S1, the temperature of the oxidation reaction is from room temperature to 200°C.

[0028] Preferably, in step S2, the temperature of the dehydration reaction is 50-250°C.

[0029] Preferably, in step S3, the hydroxy compound includes one or more of tert-butyl alcohol, benzyl alcohol, diethylene glycol, glycerol, erythrotetraol, and water.

[0030] Preferably, in step S3, the metal alkaline catalyst includes one or two of stannous octoate, sodium methoxide, potassium tert-butoxide, and antimony glycolate.

[0031] Preferably, in step S3, the reaction temperature of the polymerization process is -50 to 300°C.

[0032] In a second aspect of the present invention, a product is provided, which is a plastic product made of polyhydroxy ester synthesized by oxidation using alcohol and air.

[0033] Beneficial effects:

[0034] Compared to traditional bacterial fermentation methods, this method can directly utilize simple, readily available alcohols to synthesize the monomers required for polyhydroxy acids, avoiding the high costs associated with traditional bacterial fermentation methods, the difficulty in controlling and purifying the resulting single hydroxy acid, and competition with human food. Furthermore, the present method for synthesizing polyhydroxy acid esters using alcohol and air oxidation allows for the synthesis of the desired hydroxy acid salt by controlling the type of alcohol. This overcomes the operational inconvenience and high costs associated with traditional bacterial fermentation methods, which require controlling the type of bacteria or enzymes, or even inserting different gene fragments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The H NMR spectra of the oxidation product of Example 1, 1,2-propylene glycol and pure sodium lactate;

[0036] Figure 2 The H NMR spectra of lactide before purification (top) and after purification (bottom) in Example 1;

[0037] Figure 3 This is the hydrogen nuclear magnetic resonance spectrum of the polylactic acid of Example 1.

[0038] Figure 4 This is the hydrogen nuclear magnetic resonance spectrum of the oxidation product of Comparative Example 1;

[0039] Figure 5 This is the hydrogen nuclear magnetic resonance spectrum of the oxidation product of Comparative Example 2; DETAILED DESCRIPTION

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive work.

[0041] The present invention proposes a method for synthesizing polyhydroxy esters by oxidation of alcohol and air, wherein low-cost monohydric alcohol or dihydric alcohol is used as raw material to prepare polyhydroxy ester plastics. The specific steps are as follows:

[0042] S1. In an oxygen atmosphere, a monohydric alcohol and / or a dihydric alcohol is oxidized and reacts with a base to form a hydroxy acid salt;

[0043] Specifically, diols include:

[0044]

[0045] and / or,

[0046]

[0047] Monohydric alcohols include:

[0048]

[0049] Wherein, R1, R3, and R5 are independent of each other and are all hydrogen or alkyl, R2 is a saturated carbon chain of C1-C5, and R4 is a saturated carbon chain of C3-C4.

[0050] Preferably, in step S1, under the action of a synergistic catalyst, the monohydric alcohol and / or dihydric alcohol is oxidized and reacts with a base to form a hydroxy acid salt; more preferably, the molar ratio of the substrate alcohol to the base is 1:(0.1-10).

[0051] Among them, the synergistic catalyst includes a main catalyst and a co-catalyst. The main catalyst includes Group VIII transition metals, copper sub-group metals, zinc sub-group metals, and Group IIIA-VIA metals. The co-catalyst is a reactive ligand, including a phosphine or nitrogen ligand.

[0052] Preferably, the amount of the main catalyst in the cooperative catalyst is 0.01 to 10% of the molar amount of the substrate alcohol.

[0053] Preferably, the molar ratio of the main catalyst to the co-catalyst is 1:(0.1-10).

[0054] Specifically, the main catalyst includes metal halides, acetates, sulfates, nitrates, etc. of ruthenium, rhodium, palladium, iron, cobalt, nickel, copper, zinc, gold, etc. Preferably, it can be selected from one or more of ruthenium trichloride, ferric chloride, cobalt trichloride, rhodium trichloride, gold trichloride, palladium chloride, copper chloride, zinc chloride, rhodium acetate, etc.

[0055] Specifically, the co-catalyst includes one or more of triphenylphosphine, triphenylphosphine oxide, tri-tert-butylphosphine, tricyclohexylphosphine, bis(2-diphenylphosphine)phenyl ether, 2,2,6,6-tetramethylpiperidinyl oxide, 2,2'-bipyridine, ethylenediamine, o-phenanthroline, and the like.

[0056] In step S1, the cooperative catalyst can effectively catalyze the selective oxidation of alcohols by combining the reactive ligand with the metal center, thereby ensuring the selectivity of monohydric alcohols or dihydric alcohols.

[0057] Monohydric alcohol / dihydric alcohol and air undergo oxidation reaction under the action of synergistic catalyst and base. This oxidation reaction is based on the selective oxidation of monohydric alcohol or dihydric alcohol. There are three possible oxidation possibilities, as follows:

[0058] The general formula for the oxidation reaction of the diol of formula (I) is as follows:

[0059]

[0060] The general formula for the oxidation reaction of the diol of formula (II) is as follows:

[0061]

[0062] The general formula for the oxidation reaction of the monohydric alcohol of formula (III) is as follows:

[0063]

[0064] In reaction (I) and reaction (II), the purpose of adding a base during the reaction is to cause the dicarbonyl compound produced during the reaction to undergo a self-disproportionation reaction to obtain the hydroxy acid salt of the main reaction; in reaction (III), the purpose of adding a base is to convert the mixture of hemiacetals or lactones formed in the reaction into the same type of hydroxy acid salt. This process is irreversible, thereby increasing the yield of the target product hydroxy acid salt.

[0065] In the reaction of step S1, if no base is added, an unfavorable reaction will occur during the oxidation process, and the general formula is as follows:

[0066] The general formula of the unfavorable reaction during the oxidation of the diol of formula (I) is as follows:

[0067]

[0068] The general formulas for the unfavorable reactions during the oxidation of the diol of formula (II) are as follows: Reaction (V) and Reaction (VI):

[0069] When R2 is an alkyl chain with 1 carbon atom, reaction (V):

[0070]

[0071] When R2 is an alkyl chain with 2 to 5 carbon atoms, reaction (VI):

[0072]

[0073] The general formula of the unfavorable reaction during the oxidation of the diol of formula (III) is as follows:

[0074]

[0075] Preferably, in step S1, the base includes one or more hydroxides, carbonates, or nitrogen-containing compounds. Specifically, the base includes one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, tetramethylammonium hydroxide, and the like. Byproducts or intermediates produced during the reaction in step S1 undergo self-disproportionation or alkaline hydrolysis under the action of the base, converting them into the target product, hydroxy acid salt, thereby improving the conversion rate and selectivity of the oxidation reaction in step S1.

[0076] Preferably, in step S1, the aerobic atmosphere can be an oxygen atmosphere or an air atmosphere, where oxygen is a clean oxidant. More preferably, the oxidation reaction is carried out in a safer air atmosphere. The air pressure is controlled to be 1 to 50 atm, and the air flow rate is 0 to 10 L / min, more preferably, the air flow rate is 0.6 to 1 L / min.

[0077] Preferably, in step S1, the reaction is controlled to be at room temperature to 200° C., and the reaction time is 1 to 48 hours. It is easy to understand that the reaction temperature can be higher than the melting point of the monohydric alcohol or dihydric alcohol under the corresponding reaction pressure to increase the oxidation reaction rate, but the temperature should not be too high to avoid reducing the oxidation reaction conversion rate and selectivity.

[0078] S2. The hydroxy acid salt obtained in step S1 is mixed with an acid for neutralization to form a hydroxy acid, which is then heated and dehydrated to obtain an intermediate product, which is a lactone or a lactide.

[0079] The structural formula of lactide formed by dehydration of the hydroxy acid obtained by oxidation of the diol of formula (I) is as follows:

[0080]

[0081] The lactone or lactide formed by dehydration of the hydroxy acid obtained by oxidation of the diol of formula (II) or the monool of formula (III) has the following structural formula:

[0082]

[0083] Wherein, R1, R, and R' are independent of each other, R1 is hydrogen or an alkyl group, R is the above-mentioned R2 or R4, and R' is the above-mentioned H or R3.

[0084] It is easy to understand that in step S2, the acid (HB) used for the neutralization reaction must be stronger than the acidity of the hydroxy acid (HA) corresponding to the hydroxy acid salt to be produced, that is, pKa (HB) < pKa (HA), so that the neutralization reaction can occur to produce the hydroxy acid. Preferably, the acid includes one or more non-oxidizing strong acids such as hydrochloric acid, dilute sulfuric acid, and phosphoric acid. Preferably, to ensure sufficient reaction and improve reaction efficiency, the molar ratio of hydroxy acid salt to acid for neutralization reaction is preferably 1: (1 to 10), and the reaction temperature is preferably room temperature.

[0085] Preferably, in step S2, the dehydration reaction temperature is 50-250°C. The temperature during the dehydration process should not be too high to reduce the release of the corresponding hydroxy acid or its resulting lactide or lactone along with the water molecules. More preferably, the dehydration reaction pressure is 0.0001-1 atm, and the reaction time is 0.5-12 hours.

[0086] S3. The intermediate product obtained in step S2 is polymerized under the action of a metal alkaline catalyst and a hydroxy compound initiator to obtain polyhydroxy acid ester.

[0087] In step S3, the metal alkaline catalyst includes one or more metal alkoxides and / or organic acid salt compounds of tin, titanium, zinc, aluminum, potassium, sodium, lithium, copper, iron, or antimony, specifically one or two selected from stannous octoate, sodium methoxide, potassium tert-butoxide, and antimony glycolate. The hydroxyl compound includes an alcohol and / or water, specifically one or more selected from tert-butanol, benzyl alcohol, diethylene glycol, glycerol, erythrobutylene glycol, and water.

[0088] Preferably, the reaction molar ratio of the intermediate product in step S2, the metal alkaline catalyst and the hydroxy compound initiator is (50-2000):1:(0.1-10).

[0089] In step S3, the polymerization process follows the coordination insertion mechanism, and the corresponding cyclic ester (lactone) or lactide breaks the acyloxy bond under the action of the metal alkoxide, and then repeatedly achieves chain growth, and finally forms a hydroxy acid in the presence of a hydroxy compound.

[0090] Preferably, in step S3, the reaction temperature of the polymerization process is -50 to 300° C., and the pressure is 0.0001 to 1 atm.

[0091] It is easy to understand that after the polymerization reaction in step S3 is completed, purification treatment is further included. The present invention does not limit the specific purification treatment.

[0092] The present invention directly utilizes low-cost monohydric or dihydric alcohols to synthesize polyhydroxy esters, resulting in a simple preparation process and reduced synthesis costs. Furthermore, the chirality of the monohydric or dihydric alcohol can be used to control the chirality of the resulting polyhydroxy ester, avoiding the high costs, complex purification, and difficulty in controlling chirality associated with traditional biofermentation methods. The polyhydroxy esters produced by the present invention can be directly used to prepare biodegradable plastic products, helping to alleviate existing white pollution.

[0093] The technical solutions of the present invention are described in detail below with reference to specific examples. Unless otherwise specified, the raw materials used in the following examples and comparative examples are commercially available. Furthermore, nuclear magnetic resonance spectroscopy of hydroxy acid salts and molecular weight analysis of polyhydroxy acid are performed in the following manner.

[0094] MRI test steps: 1 H. 13 C nuclear magnetic resonance spectroscopy (NMR) was performed on a Bruker AVANCE NEO 600 MHz spectrometer. Deuterated chloroform or heavy water was usually used as the solvent.

[0095] Molecular weight test steps: Gel permeation chromatography (GPC, model PL-GPC 220) was used to detect the number average molecular weight and molecular weight distribution of the polymerization product.

[0096] Example 1

[0097] S1. Oxidation Reaction: 35 g of 1,2-propylene glycol and 18.4 g of sodium hydroxide were added to a 250 mL reactor, with the molar ratio of left-handed 1,2-propylene glycol (hereinafter referred to as the same) to sodium hydroxide being 1:1. 0.1908 g of ruthenium trichloride (RuCl3) and 0.7680 g of triphenylphosphine oxide (O=P(Ph)3) were then added. A catalytic oxidation reaction was conducted at 20 atm with stirring, while flowing compressed air at a flow rate of 1 L / min. The reaction was heated to 150°C for 8 hours.

[0098] Comparison of oxidation products, 1,2-propylene glycol and pure sodium lactate ( Figure 1 The NMR spectrum (using deuterated water as the testing solvent) shows a significant decrease in the characteristic peak of 1,2-propylene glycol in the oxidation product. The primary product is sodium lactate, with sodium acetate as the byproduct. Calculated oxidation conversion of 1,2-propylene glycol reached 92.5%, with a yield of 22.6% for the target product, sodium lactate.

[0099] S2, dehydration reaction: The oxidation product obtained in step S1 is neutralized with hydrochloric acid (mass concentration: 36%) in an equimolar ratio, then transferred to a 100 mL distillation flask and vacuumed to 100 Pa. Dehydration is carried out under reduced pressure at a temperature of 120°C and a rotation speed of 120 r / min. The reaction is continued for 3 hours to obtain oligomeric lactic acid and lactide. Subsequently, the receiving flask is replaced, the temperature is raised to 230°C, the oligomeric lactic acid is cracked, and the distillate is collected. Purification is continued, and the distillate obtained by vacuum distillation is recrystallized twice with ethanol and once with ethyl acetate to obtain polymerization-grade L-lactide. Figure 2 As shown, after NMR detection, lactide with a purity of 99% was obtained after step S2.

[0100] S3, polymerization reaction: In a 100mL eggplant-shaped Schlenk flask, add 3g of polymerization-grade lactide monomer obtained in step S2, use potassium tert-butoxide as polymerization catalyst, and benzyl alcohol as initiator. The feeding molar ratio of lactide, polymerization catalyst and initiator is 200:1:1, and the ring-opening polymerization reaction is carried out at 120°C for 4 hours. After the reaction is completed and cooled naturally, chloroform is added to dissolve and filter. Then, ether is added to precipitate the polymer and filter it by suction. After separation and drying, high molecular weight left-handed polylactic acid (PLA) is obtained, and its NMR spectrum is as follows Figure 3 GPC analysis showed that the number average molecular weight of the PLA obtained in step S3 was 78.5 kDa, and the molecular weight distribution was 1.1.

[0101] Example 2

[0102] Example 2 was carried out according to the method of Example 1, with the only difference being that the levorotatory 1,2-propylene glycol in step S1 was replaced by n-butanol.

[0103] S1 Oxidation Reaction: 40 g of n-butanol and 21.6 g of sodium hydroxide were added to a 250 mL reactor, with a molar ratio of n-butanol to sodium hydroxide of 1:1. 0.2240 g of ruthenium trichloride (RuCl3) and 0.9016 g of triphenylphosphine oxide (O=P(Ph)3) were then added. Under stirring conditions at a pressure of 20 atm, a flow of compressed air at a flow rate of 1 L / min was introduced, and the mixture was heated to 150°C for 8 hours to carry out a catalytic oxidation reaction to obtain an oxidation product. The calculated oxidation conversion of n-butanol was 86.1%, with a yield of 32.2% for the target product, sodium 4-hydroxybutyrate.

[0104] Dehydration reaction S2: The oxidation product obtained in step S1 was neutralized with an equimolar ratio of hydrochloric acid, transferred to a 100 mL distillation flask, and the pressure was reduced to 100 Pa. Dehydration was then carried out under reduced pressure at 90°C and 120 rpm for 3 hours to yield oligomeric 4-hydroxybutyrate and γ-butyrolactone. The receiving flask was then replaced, the temperature was raised to 210°C for cracking, and the distillate was collected. Purification was continued, and the distillate was further purified by two more rounds of reduced pressure distillation to obtain polymer-grade γ-butyrolactone with a purity of 99%.

[0105] S3 polymerization reaction: In a 100 mL eggplant-shaped Schlenk flask, 3 g of polymerization-grade γ-butyrolactone monomer obtained in step S2 was added, potassium tert-butoxide was used as a polymerization catalyst, and benzyl alcohol was used as an initiator. The molar ratio of γ-butyrolactone, polymerization catalyst, and initiator was 200:1:1, and a ring-opening polymerization reaction was carried out at -50 ° C for 4 hours. After the reaction was completed, chloroform was added to dissolve and filter. Ether was then added to precipitate the polymer and filtered, separated and dried to obtain high molecular weight poly γ-butyrolactone, i.e., poly 4-hydroxybutyrate. GPC detection showed that the number average molecular weight of the poly 4-hydroxybutyrate obtained in step S3 was 44.9 kDa, and the molecular weight distribution was 1.2.

[0106] Example 3

[0107] Example 2 was carried out according to the method of Example 1, with the only difference being that the levorotatory 1,2-propylene glycol in step S1 was replaced by n-pentanol.

[0108] S1 Oxidation Reaction: 40 g of n-pentanol and 18.2 g of sodium hydroxide were added to a 250 mL reactor at a molar ratio of 1:1. 0.1883 g of ruthenium trichloride (RuCl3) and 0.7580 g of triphenylphosphine oxide (O=P(Ph)3) were then added. Under stirring conditions at 20 atm, a flow of compressed air at a flow rate of 1 L / min was introduced, and the mixture was heated to 150°C for 8 hours to carry out a catalytic oxidation reaction to obtain an oxidation product. The calculated oxidation conversion of n-pentanol was 72.4%, with a yield of 19.2% for the target product, δ-valerolactone.

[0109] Dehydration reaction S2: The oxidation product obtained in step S1 was neutralized with an equimolar ratio of hydrochloric acid, transferred to a 100 mL distillation flask, and the pressure was reduced to 100 Pa. Dehydration was then carried out under reduced pressure at 90°C and 120 rpm for 3 hours to yield oligomeric 5-hydroxyvalerate and δ-valerolactone. The receiving flask was then replaced, the temperature was raised to 220°C for cracking, and the distillate was collected. Purification was continued, and the distillate was further purified by two more rounds of reduced pressure distillation to obtain polymer-grade δ-valerolactone with a purity of 99%.

[0110] S3 polymerization reaction: In a 100 mL eggplant-shaped Schlenk flask, 3 g of polymerization-grade δ-valerolactone monomer obtained in step S2 was added, potassium tert-butoxide was used as a polymerization catalyst, and benzyl alcohol was used as an initiator. The molar ratio of δ-valerolactone, polymerization catalyst, and initiator was 200:1:1, and a ring-opening polymerization reaction was carried out at 20°C for 8 hours. After the reaction was completed and the temperature was naturally lowered, chloroform was added to dissolve and filter. Ether was then added to precipitate the polymer and filtered, separated, and dried to obtain high molecular weight polyδ-valerolactone. GPC analysis showed that the number average molecular weight of the poly 5-hydroxyvalerate obtained in step S3 was 44.9 kDa, and the molecular weight distribution was 1.3.

[0111] Example 4

[0112] Example 2 was carried out according to the method of Example 1, with the only difference being that ethylene glycol was replaced by levorotatory 1,2-propylene glycol in step S1.

[0113] S1 Oxidation Reaction: 45 g of ethylene glycol and 29.0 g of sodium hydroxide were added to a 250 mL reactor at a molar ratio of 1:1. 0.3008 g of ruthenium trichloride (RuCl3) and 1.2105 g of triphenylphosphine oxide (O=P(Ph)3) were then added. Under stirring conditions at 20 atm, a flow of compressed air at a rate of 1 L / min was introduced, and the mixture was heated to 150°C for a catalytic oxidation reaction for 8 hours. The calculated oxidation conversion of ethylene glycol was 90.0%, with a yield of 26.7% for the target product, sodium glycolate.

[0114] Dehydration Reaction S2: The oxidation product obtained in Step S1 was neutralized with an equimolar ratio of hydrochloric acid, transferred to a 100 mL distillation flask, and decompressed to 100 Pa. Dehydration was then performed at 120°C and 120 rpm for 3 hours to yield oligomeric glycolic acid and glycolide. The receiving flask was then replaced, and the temperature was raised to 250°C for cracking and collection of the distillate. Further purification was continued, and the distillate was recrystallized from acetone, isopropanol, and ethyl acetate to yield 99% polymer-grade glycolide.

[0115] S3 polymerization reaction: In a 100 mL eggplant-shaped Schlenk flask, 3 g of polymerization-grade glycolide monomer obtained in step S2 was added, potassium tert-butoxide was used as a polymerization catalyst, and benzyl alcohol was used as an initiator. The feeding molar ratio of glycolide, polymerization catalyst and initiator was 200:1:1, and a ring-opening polymerization reaction was carried out at 120 ° C for 4 hours. After the reaction was completed and the temperature was naturally lowered, chloroform was added to dissolve and filter. Then, ether was added to precipitate the polymer and filtered, separated and dried to obtain high molecular weight polyglycolic acid. GPC detection showed that the number average molecular weight of the polyglycolic acid obtained in step S3 was 54.6 kDa, and the molecular weight distribution was 1.2.

[0116] Example 5

[0117] Example 2 was carried out according to the method of Example 1, with the only difference being that the levorotatory 1,2-propylene glycol in step S1 was replaced by 1,3-butanediol.

[0118] S1 Oxidation Reaction: 40 g of 1,3-butanediol and 17.55 g of sodium hydroxide were added to a 250 mL reactor at a molar ratio of 1:1. 0.1841 g of ruthenium trichloride (RuCl3) and 0.7411 g of triphenylphosphine oxide (O=P(Ph)3) were then added. Under stirring conditions at 20 atm, a flow of compressed air at a flow rate of 1 L / min was introduced. The mixture was heated to 150°C for 8 hours to carry out a catalytic oxidation reaction to obtain an oxidation product. The calculated oxidation conversion of 1,3-butanediol was 72.4%, with a yield of 21.2% for the target product, sodium 3-hydroxybutyrate.

[0119] Dehydration reaction S2: The oxidation product obtained in step S1 is neutralized with an equimolar ratio of hydrochloric acid, transferred to a 100 mL distillation flask, and the pressure is reduced to 100 Pa. Dehydration is then carried out under reduced pressure at 90°C and 120 rpm for 3 hours to yield oligomeric 3-hydroxybutyrate and β-butyrolactone. The receiving flask is then replaced, the temperature is raised to 140°C for cracking, and the distillate is collected. Purification is continued, and the distillate is further purified by two more rounds of reduced pressure distillation to obtain polymer-grade β-butyrolactone with a purity of 99%.

[0120] S3 polymerization reaction: In a 100 mL eggplant-shaped Schlenk flask, 3 g of polymerization-grade β-butyrolactone monomer obtained in step S2 was added, potassium tert-butoxide was used as a polymerization catalyst, and benzyl alcohol was used as an initiator. The molar ratio of β-butyrolactone, polymerization catalyst, and initiator was 200:1:1, and a ring-opening polymerization reaction was carried out at 120 ° C for 4 hours. After the reaction was completed and cooled naturally, chloroform was added to dissolve and filter. Then, ether was added to precipitate the polymer and filtered, separated and dried to obtain high molecular weight poly 3-hydroxybutyrate. GPC detection showed that the number average molecular weight of the poly 3-hydroxybutyrate obtained in step S3 was 46.8 kDa, and the molecular weight distribution was 1.2.

[0121] Example 6

[0122] Example 2 was carried out according to the method of Example 1, with the only difference being that the levorotatory 1,2-propanediol in step S1 was replaced by 1,4-pentanediol.

[0123] S1 Oxidation Reaction: 40 g of 1,4-pentanediol and 15.36 g of sodium hydroxide were added to a 250 mL reactor at a molar ratio of 1:1. 0.1593 g of ruthenium trichloride (RuCl3) and 0.6413 g of triphenylphosphine oxide (O=P(Ph)3) were then added. Under stirring conditions at a pressure of 20 atm, a flow of compressed air at a flow rate of 1 L / min was introduced, and the mixture was heated to 150°C for 8 hours for a catalytic oxidation reaction to obtain an oxidation product. The calculated oxidation conversion of 1,4-pentanediol was 92.7%, with a yield of 34.2% for the target product, sodium 5-hydroxyvalerate.

[0124] Dehydration reaction S2: The oxidation product obtained in step S1 was neutralized with an equimolar ratio of hydrochloric acid, transferred to a 100 mL distillation flask, and the pressure was reduced to 100 Pa. Dehydration was then carried out under reduced pressure at 90°C and 120 rpm for 3 hours to yield oligomeric 5-hydroxyvalerate and δ-valerolactone. The receiving flask was then replaced, the temperature was raised to 110°C for cracking, and the distillate was collected. Purification was continued, and the distillate was further purified by two more rounds of reduced pressure distillation to obtain δ-valerolactone with a purity of 99%.

[0125] S3 polymerization reaction: In a 100 mL eggplant-shaped Schlenk flask, 3 g of polymerization-grade δ-valerolactone monomer obtained in step S2 was added, potassium tert-butoxide was used as a polymerization catalyst, and benzyl alcohol was used as an initiator. The molar ratio of δ-valerolactone, polymerization catalyst, and initiator was 200:1:1, and a ring-opening polymerization reaction was carried out at 185°C for 8 hours. After the reaction was completed and the temperature was naturally lowered, chloroform was added to dissolve and filter. Ether was then added to precipitate the polymer and filtered, separated, and dried to obtain high molecular weight poly 5-hydroxyvalerate. GPC analysis showed that the number average molecular weight of the poly 5-hydroxyvalerate obtained in step S3 was 41.3 kDa, and the molecular weight distribution was 1.3.

[0126] Example 7

[0127] Example 1 was carried out according to the method of Example 1, with the only difference being that the temperature in step S1 was replaced with 180°C.

[0128] A 250mL reactor was charged with 35g of 1,2-propylene glycol and 18.4g of sodium hydroxide at a 1:1 molar ratio. 0.1908g of ruthenium trichloride (RuCl3) and 0.7680g of triphenylphosphine oxide (O=P(Ph)3) were then added. A catalytic oxidation reaction was carried out at 180°C for 8 hours under stirring and a flow rate of 1L / min of compressed air at 20atm. The calculated 1,2-propylene glycol oxidation conversion reached 97.7%, with a yield of 30.5% for the target product, sodium lactate.

[0129] Example 8

[0130] Example 8 was carried out according to the method of Example 1, with the only difference being that the pressure of 20 atm in step S1 was replaced by 30 atm.

[0131] A 250mL reactor was charged with 35g of 1,2-propylene glycol and 18.4g of sodium hydroxide at a 1:1 molar ratio. 0.1908g of ruthenium trichloride (RuCl3) and 0.7680g of triphenylphosphine oxide (O=P(Ph)3) were then added. Under stirring conditions at 30atm, a stream of compressed air was introduced at a flow rate of 1L / min and the reaction was heated to 150°C for 8 hours for a catalytic oxidation reaction. The calculated oxidation conversion of 1,2-propylene glycol reached 95.4%, with a yield of 25.4% for the target product, sodium lactate.

[0132] Example 9

[0133] Example 9 was carried out according to the method of Example 1, with the only difference being that the flow of compressed air in step S1 was set at a flow rate of 5 L / min.

[0134] A 250mL reactor was charged with 35g of 1,2-propylene glycol and 18.4g of sodium hydroxide at a molar ratio of 1:1. 0.1908g of ruthenium trichloride (RuCl3) and 0.7680g of triphenylphosphine oxide (O=P(Ph)3) were then added. Under stirring conditions at 20atm, a stream of compressed air was introduced at a flow rate of 5L / min and the reaction was heated to 150°C for 8 hours for a catalytic oxidation reaction. The calculated oxidation conversion of 1,2-propylene glycol reached 93.8%, with a yield of 23.8% for the target product, sodium lactate.

[0135] Example 10

[0136] Example 10 was carried out according to the method of Example 1, with the only difference being that the catalyst ruthenium trichloride in step S1 was replaced by rhodium acetate.

[0137] S1 oxidation reaction

[0138] A 250 mL reactor was charged with 35 g of 1,2-propylene glycol and 18.4 g of sodium hydroxide at a 1:1 molar ratio. 0.2576 g of rhodium acetate and 0.7680 g of triphenylphosphine oxide were then added. Under stirring conditions at 20 atm, a flow of compressed air at a rate of 1 L / min was introduced, and the reaction was heated to 150°C for 8 hours for a catalytic oxidation reaction. The calculated 1,2-propylene glycol oxidation conversion reached 95.6%, with a yield of 27.6% for the target product, sodium lactate.

[0139] Example 11

[0140] Example 11 was carried out according to the method of Example 1, with the only difference being that the catalyst ruthenium trichloride in step S1 was replaced by palladium chloride.

[0141] S1 oxidation reaction

[0142] A 250 mL reactor was charged with 35 g of 1,2-propylene glycol and 18.4 g of sodium hydroxide at a 1:1 molar ratio. 0.1631 g of palladium chloride and 0.7680 g of triphenylphosphine oxide were then added. Under stirring conditions at 20 atm, a compressed air flow at a rate of 1 L / min was introduced, and the reaction was heated to 150°C for 8 hours for a catalytic oxidation reaction. The calculated conversion of 1,2-propylene glycol reached 94.6%, with a yield of 22.1% for the target product, sodium lactate.

[0143] Example 12

[0144] Example 12 was carried out according to the method of Example 1, with the only difference being that the co-catalyst triphenylphosphine oxide in step S1 was replaced by 2,2,6,6-tetramethylpiperidine nitrogen oxide.

[0145] S1 oxidation reaction

[0146] A 250mL reactor was charged with 35g of 1,2-propylene glycol and 18.4g of sodium hydroxide at a 1:1 molar ratio. 0.1908g of ruthenium trichloride (RuCl3) and 0.4312g of 2,2,6,6-tetramethylpiperidinium nitroxide (TEMPO) were then added. Under stirring conditions at 20atm, a stream of compressed air was introduced at a flow rate of 1L / min and the reaction was heated to 150°C for 8 hours for catalytic oxidation. The calculated 1,2-propylene glycol oxidation conversion reached 92.8%, with a yield of 19.3% for the target product, sodium lactate.

[0147] Example 13

[0148] Example 13 was carried out according to the method of Example 1, with the only difference being that the co-catalyst triphenylphosphine oxide in step S1 was replaced by triphenylphosphine.

[0149] S1 oxidation reaction

[0150] A 250mL reactor was charged with 35g of 1,2-propylene glycol and 18.4g of sodium hydroxide at a 1:1 molar ratio. 0.1908g of ruthenium trichloride (RuCl3) and 0.7239g of triphenylphosphine were then added. Under stirring conditions at 20atm, a compressed air flow at a rate of 1L / min was introduced, and the reaction was heated to 150°C for 8 hours for a catalytic oxidation reaction. The calculated oxidation conversion of 1,2-propylene glycol reached 92.7%, with a yield of 23.5% for the target product, sodium lactate.

[0151] Example 14

[0152] Example 14 was carried out according to the method of Example 1, with the only difference being that the 36% hydrochloric acid in step S2 was replaced by 60% dilute sulfuric acid.

[0153] S2 dehydration reaction

[0154] The oxidation product obtained in step S1 was neutralized with an equimolar ratio of dilute sulfuric acid, then transferred to a 100 mL distillation flask, where the pressure was reduced to 100 Pa. Dehydration was then performed at 120°C and 120 rpm for 3 hours to yield oligomeric lactic acid and lactide. The receiving flask was then replaced, the temperature was raised to 230°C for cracking, and the distillate was collected. Purification continued, with the distillate being recrystallized twice from ethanol and once from ethyl acetate to obtain polymerization-grade lactide. NMR analysis revealed that lactide with a purity of 99% was obtained after step S2.

[0155] Example 15

[0156] Example 15 was carried out according to the method of Example 1, with the only difference being that potassium tert-butoxide in step S3 was replaced by stannous octoate.

[0157] S3 polymerization reaction

[0158] In a 100 mL eggplant-shaped Schlenk flask, 3 g of polymer-grade lactide monomer obtained in step S2 was added, with stannous octoate as a polymerization catalyst and benzyl alcohol as an initiator. The molar ratio of lactide, polymerization catalyst, and initiator was 200:1:1, and a ring-opening polymerization reaction was carried out at 120°C for 4 hours. After the reaction was completed and the temperature was naturally lowered, chloroform was added to dissolve and filter. Ether was then added to precipitate the polymer and filtered, separated, and dried to obtain high molecular weight polylactic acid (PLA). GPC analysis showed that the number average molecular weight of the PLA obtained in step S3 was 98.8 kDa, with a molecular weight distribution of 1.3.

[0159] Example 16

[0160] Example 16 was carried out according to the method of Example 1, with the only difference being that potassium tert-butoxide in step S3 was replaced by antimony ethylene glycol.

[0161] S3 polymerization reaction

[0162] To a 100 mL eggplant-shaped Schlenk flask, add 3 g of polymer-grade lactide monomer obtained in step S2, ethylene glycol antimony as the polymerization catalyst, and water as the initiator. The molar ratio of lactide, polymerization catalyst, and initiator is 200:1:1, and ring-opening polymerization is carried out at 120°C for 4 hours. After the reaction is complete and the temperature is naturally cooled, chloroform is added to dissolve the mixture, the mixture is filtered, and then diethyl ether is added to precipitate the polymer. GPC analysis shows that the number average molecular weight of the PLA obtained in step S3 is 79.4 kDa, with a molecular weight distribution of 1.2.

[0163] Example 17

[0164] Example 17 was carried out according to the method of Example 1, with the only difference being that the reaction temperature in step S3 was replaced with 150°C.

[0165] S3 polymerization reaction

[0166] To a 100 mL eggplant-shaped Schlenk flask, add 3 g of polymer-grade lactide monomer obtained in step S2, potassium tert-butoxide as a polymerization catalyst, and benzyl alcohol as an initiator. The molar ratio of lactide, polymerization catalyst, and initiator is 200:1:1, and ring-opening polymerization is carried out at 150°C for 4 hours. After the reaction is complete and the temperature is naturally lowered, chloroform is added to dissolve the mixture, the mixture is filtered, and diethyl ether is added to precipitate the polymer. GPC analysis shows that the number average molecular weight of the PLA obtained in step S3 is 91.2 kDa, with a molecular weight distribution of 1.5.

[0167] Example 18

[0168] Example 18 was carried out according to the method of Example 1, except that the benzyl alcohol in step S3 was replaced by water.

[0169] S3 polymerization reaction

[0170] To a 100 mL eggplant-shaped Schlenk flask, add 3 g of polymer-grade lactide monomer obtained in step S2, potassium tert-butoxide as the polymerization catalyst, and water as the initiator. The molar ratio of lactide, polymerization catalyst, and initiator is 200:1:1, and ring-opening polymerization is carried out at 120°C for 4 hours. After the reaction is complete and the temperature is naturally lowered, chloroform is added to dissolve the mixture, the mixture is filtered, and diethyl ether is added to precipitate the polymer. GPC analysis shows that the number average molecular weight of the PLA obtained in step S3 is 85.4 kDa, with a molecular weight distribution of 1.2.

[0171] Comparative Example 1

[0172] Comparative Example 1 was carried out according to the method of Example 1, except that the sodium hydroxide in step S1 was replaced with a blank.

[0173] In a 250 mL reactor, 35 g of 1,2-propylene glycol was added, followed by 0.1908 g of ruthenium trichloride (RuCl3) and 0.7680 g of triphenylphosphine oxide (O=P(Ph)3). Under a pressure of 20 atm and stirring conditions, a flow of compressed air was introduced at a flow rate of 1 L / min, and the reaction was heated to 150°C for catalytic oxidation for 8 hours. Figure 4 As shown, NMR analysis shows that the oxidation conversion rate of 1,2-propylene glycol in the absence of alkali is only 39.8%. Furthermore, due to chain scission side reactions, the main oxidation product is acetic acid, with a yield of 13.1% and an acetic acid to lactic acid ratio of 1.9:1. In contrast, in Example 1, the yield of sodium acetate is 9.0%, and the ratio of sodium acetate to sodium lactate is 0.4:1.

[0174] Comparative Example 2

[0175] Comparative Example 2 was carried out according to the method of Example 1, except that the molar ratio of 1:1 of levorotatory 1,2-propylene glycol to sodium hydroxide in step S1 was replaced by 1:0.25.

[0176] A 250 mL reactor was charged with 35 g of 1,2-propylene glycol and 4.60 g of sodium hydroxide (1:0.25 molar ratio). Then, 0.1908 g of ruthenium trichloride (RuCl3) and 0.7680 g of triphenylphosphine oxide (O=P(Ph)3) were added. A catalytic oxidation reaction was conducted at 150°C for 8 hours under stirring and a flow rate of 1 L / min of compressed air at 20 atm.

[0177] Figure 5The H NMR spectrum of the oxidation product from Comparative Example 2 is shown. When the amount of sodium hydroxide was reduced to 0.25 equivalents of 1,2-propylene glycol, the main product had converted to sodium acetate. Calculated, the oxidation conversion of 1,2-propylene glycol decreased to 74.7%, with a yield of 14.6% for the target product, sodium lactate. The yield of sodium acetate increased to 26.4%, with a sodium acetate to sodium lactate ratio of 1.8:1.

[0178] In summary, the present method for synthesizing polyhydroxy acid esters using alcohol and air oxidation and the products thereof, compared to traditional bacterial fermentation methods, can directly utilize simple, readily available alcohols to synthesize the monomers required for producing polyhydroxy acid. This avoids the high costs associated with traditional bacterial fermentation methods, the difficulty in controlling and purifying the resulting single hydroxy acid, and competition with human food supply. Furthermore, the present method for synthesizing polyhydroxy acid esters using alcohol and air oxidation allows for the synthesis of the desired hydroxy acid salt by controlling the type of alcohol, overcoming the operational inconvenience and high costs associated with traditional bacterial fermentation methods, which require controlling the type of bacteria or enzymes, or even inserting different gene fragments.

[0179] The embodiments provided by the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for synthesizing polyhydroxy esters by oxidation using alcohol and air, characterized in that: Here are the steps: S1. In an oxygen atmosphere, a monohydric alcohol and / or a dihydric alcohol is oxidized and reacts with a base to form a hydroxy acid salt; S2, neutralizing the hydroxy acid salt obtained in step S1 with an acid to form a hydroxy acid, and then dehydrating the hydroxy acid to obtain an intermediate product; S3, polymerizing the intermediate product obtained in step S2 under the action of a metal alkaline catalyst and a hydroxy compound initiator to obtain a polyhydroxy acid ester; Among them, diols include: and / or, Monohydric alcohols include: The metal alkaline catalyst includes one or more metal alkoxides and / or organic acid salt compounds of tin, titanium, zinc, aluminum, potassium, sodium, lithium, copper, iron, and antimony, and the hydroxyl compound includes alcohols and / or water.

2. The method for synthesizing polyhydroxy esters by oxidation using alcohol and air according to claim 1, characterized in that: In step S1, under the action of a synergistic catalyst, a monohydric alcohol and / or a dihydric alcohol is oxidized and reacts with a base to form a hydroxy acid salt; Among them, the synergistic catalyst includes a main catalyst and a co-catalyst, the metal elements in the main catalyst include Group VIII transition metals, copper subgroup metals, zinc subgroup metals, and Group IIIA-VIA metals, and the co-catalyst includes phosphine and / or nitrogen-based ligands.

3. The method for synthesizing polyhydroxy esters by oxidation using alcohol and air according to claim 2, characterized in that: The main catalyst includes one or more metal halides, acetates, sulfates and nitrates of ruthenium, rhodium, palladium, iron, cobalt, nickel, copper, zinc and gold, and the co-catalyst includes one or more of triphenylphosphine, triphenylphosphine oxide, tri-tert-butylphosphine, tricyclohexylphosphine, bis(2-diphenylphosphine)phenyl ether, 2,2,6,6-tetramethylpiperidinyl oxide, 2,2'-bipyridine, ethylenediamine and o-phenanthroline; Preferably, the main catalyst includes one or more of ruthenium trichloride, rhodium acetate, ferric chloride, cobalt trichloride, rhodium trichloride, gold trichloride, palladium chloride, copper chloride and zinc chloride.

4. The method for synthesizing polyhydroxy esters by oxidation using alcohol and air according to claim 1, characterized in that: In step S1, the base includes one or more of a hydroxide, a carbonate, and a nitrogen-containing compound; Preferably, the base includes one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate and tetramethylammonium hydroxide.

5. The method for synthesizing polyhydroxy esters by oxidation using alcohol and air according to claim 1, characterized in that: In step S3, the hydroxy compound includes one or more of tert-butyl alcohol, benzyl alcohol, diethylene glycol, glycerol, erythrotetraol, and water.

6. The method for synthesizing polyhydroxy esters by oxidation using alcohol and air according to claim 1, characterized in that: In step S3, the metal alkaline catalyst includes one or two of stannous octoate, sodium methoxide, potassium tert-butoxide, and antimony glycolate.

7. The method for synthesizing polyhydroxy esters by oxidation using alcohol and air according to any one of claims 1 to 6, characterized in that: In step S1 , the temperature of the oxidation reaction is from room temperature to 200° C.

8. The method for synthesizing polyhydroxy esters by oxidation using alcohol and air according to any one of claims 1 to 6, characterized in that: In step S2, the temperature of the dehydration reaction is 50-250°C.

9. The method for synthesizing polyhydroxy esters by oxidation using alcohol and air according to any one of claims 1 to 6, characterized in that: In step S3, the reaction temperature of the polymerization process is -50 to 300°C.

10. A product, characterized in that The plastic product is made by synthesizing polyhydroxy ester by the method described in any one of claims 1 to 9.

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