WO2023222042A1 - Manufacturing method for high-molecular-weight polylactic acid - Google Patents

Abstract

Provided in the present invention is a manufacturing method for polylactic acid, which method comprises the following steps: taking a lactate as a monomer raw material, and subjecting same to condensation polymerization under the action of a catalyst to obtain polylactic acid. In the method, a lactate is used as a raw material, the reaction efficiency is higher than that of the conventional dehydration polycondensation of lactic acid, the production cost is reduced, and the molecular weight and economic benefits of a polymer are increased.

Description

A kind of manufacturing method of high molecular weight polylactic acid

Cross-references to related applications

This application claims the rights and interests of patent application No. 202210544466.2 filed with the State Intellectual Property Office of China on May 18, 2022, the entire contents of which are hereby incorporated by reference in their entirety.

Technical field

This application relates to the technical field of degradable material synthesis. Specifically, this application relates to a new method for manufacturing polylactic acid, especially a method for preparing polylactic acid from the polycondensation reaction of lactic acid ester monomers. In addition, the present application also relates to polylactic acid produced by this method, especially high molecular weight polylactic acid.

Background technique

Polylactic acid (PLA) is a polymer with excellent biodegradability and compatibility. The main raw material for industrial synthesis of polylactic acid is lactic acid, and lactic acid can be obtained directly from nature (such as grain fermentation). The degradation products of polylactic acid are pollution-free carbon dioxide and water, which can be realized in nature through plant photosynthesis. Green cycle. As a completely green and degradable material, polylactic acid has almost no pollution to the environment. It is mainly used as medical drugs, environmentally friendly materials, plastic daily necessities, textile and clothing fabrics, agricultural mulch films, decorations and fitness equipment. In an environment where environmental protection, green, harmonious and sustainable development are the direction of today's economic and social development, this non-toxic, harmless and non-irritating polymer material emerged as the times require.

Currently, the two main synthesis methods of polylactic acid are direct polymerization and lactide ring-opening polymerization. Both methods have their own advantages and disadvantages. The direct polymerization method mainly involves the dehydration polymerization of lactic acid to obtain polylactic acid, but deep dehydration is difficult to carry out. Generally, high boiling point solvents (such as dimethyl ether, toluene, xylene, etc.) are used to azeotrope with water to discharge water from the reaction system. This solvent can dissolve the polymer but does not participate in the reaction. The by-product lactide is brought back to the reaction system through solvent reflux to avoid the decomposition of PLA and obtain PLA with low water content and high relative molecular weight. Therefore, this method is also called azeotropic distillation method. Due to the insoluble nature of polymers, solution polymerization requires a large amount of solvent. agents and can easily cause pollution to the environment. At the same time, the use of high boiling point organic solvents will complicate the process and increase the cost of equipment. Moreover, it is relatively difficult to purify polymers, and the resulting products usually contain residual organic solvents that are difficult to remove. The molecular weight of polylactic acid produced by this direct polymerization method is often low.

Another type of direct polymerization of lactic acid is the melt polycondensation method, which means that after the oligomers formed by melt polycondensation are granulated, crystallized and dried, the oligomers are further polymerized under appropriate temperature conditions to form small Polylactic acid chains are linked together. Although the melt-solid phase polycondensation method can improve the crystallinity and relative molecular weight of PLA, this method and equipment requirements are relatively high. Generally, the reaction must be carried out under a high degree of vacuum to obtain high molecular weight PLA. In industry It is still very difficult to popularize it.

Lactide ring-opening polymerization is a method most studied by researchers. The general steps of the ring-opening polymerization method are: synthesize lactide using lactic acid as raw material, and then ring-opening polymerize lactide under different conditions to form poly(lactide). Lactic acid, the specific process flow has three steps, which are: preparation, purification and ring-opening of lactide. Although the indirect polymerization method using lactide as raw material can produce high molecular weight polylactic acid products, the steps are relatively complicated and the cost is too high.

Therefore, there is still a need to develop a low-cost, relatively simple process for providing polylactic acid, especially high molecular weight polylactic acid.

Contents of the invention

In view of the shortcomings of the existing technology, this application provides a manufacturing method with low cost, simple process and capable of obtaining high molecular weight polylactic acid.

In order to achieve the above objectives, this application first provides a new method for manufacturing polylactic acid in one aspect, in which a polylactic acid ester monomer is subjected to a polycondensation reaction to obtain polylactic acid.

In another aspect, a method for manufacturing polylactic acid is also provided, which method includes:

a) subjecting the lactic acid ester monomer to a polycondensation reaction to obtain a polylactic acid prepolymer, and optionally, purifying the polylactic acid prepolymer;

b) Optionally, the polylactic acid prepolymer is subjected to a transesterification reaction with an exchange reagent selected from diols and dicarboxylic acids or their anhydrides, thereby forming an intermediate in which both end groups are hydroxyl or carboxyl groups. bulk polymer;

c) causing a chain extension reaction between the intermediate polymer and a chain extender to obtain high molecular weight polylactic acid.

The lactic acid ester monomer in the polycondensation reaction has the following structural formula:

Wherein R represents a substituted or unsubstituted C ₁ -C ₂₀ hydrocarbyl group or a substituted or unsubstituted C ₁ -C ₂₀ heterohydrocarbyl group. The polycondensation reaction of lactic acid ester can be carried out under the action of catalyst. The catalyst used in the polycondensation reaction is a suitable acidic or alkaline substance, and the amount is 0.01wt%-50wt% based on the amount of lactic acid ester. The polycondensation reaction can be at a temperature of 0°C to 350°C, preferably 50°C to 300°C, more preferably 100°C to 250°C, most preferably 100°C to 200°C, and/or at a temperature of 1Pa to 20MPa, preferably 10Pa to 10MPa, even more preferably It is carried out under an absolute pressure of 0.1 kPa to 1 MPa for 0.001 hours to 500 hours, for example, 1 hour to 200 hours.

Preferably, the polycondensation reaction can be carried out in steps, such as in two steps, three steps or four steps, wherein the absolute pressure in the first step is greater than or equal to atmospheric pressure, for example from 0.1MPa to 20MPa, in the second step and optionally The absolute pressure in the subsequent steps is less than atmospheric pressure, for example from 0.1 kPa to less than 0.1 MPa, and/or the temperature in the second step and optional subsequent steps is greater than or equal to the temperature in the first step.

Preferably, the polycondensation reaction is carried out in three steps, wherein the absolute pressure of the third step is less than or equal to, preferably less than the absolute pressure of the second step, and/or the temperature in the third step is greater than or equal to, preferably greater than the temperature in the second step. .

The transesterification reaction is carried out at a temperature of greater than 0°C to 300°C, such as 100°C to 200°C, for 0.01 hours to 500 hours, such as 1 hour to 100 hours.

The chain extension reaction is carried out at a temperature of greater than 0 to 300°C, such as 100°C to 200°C, for greater than 0.01 hours to 500 hours, such as 1 to 100 hours. The chain extender is one or more alcohols or amine compounds with low molecular weight polyfunctional groups containing hydroxyl or amino groups, for example, selected from diisocyanate, dioxazoline and epoxy resin, such as diphenyl Methane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), dicyclohexyl diisocyanate (HMDI), isophorone diisocyanate (IPDI), epoxy resin, preferably diphenyl Methane diisocyanate.

In yet another aspect, the present application also provides polylactic acid produced by the above method. The polylactic acid has a weight average molecular weight greater than 500; or a weight average molecular weight greater than or equal to 1,000; or a weight average molecular weight greater than 2,000; or a weight average molecular weight greater than 5,000; or a weight average molecular weight greater than 10,000. Under appropriate circumstances, the weight average molecular weight of polylactic acid can be greater than 50,000, or even greater than 100,000.

The manufacturing method of polylactic acid according to the present application has the following beneficial effects:

This method uses lactic acid ester as the monomer raw material, and directly polycondensates under the action of a catalyst to synthesize high molecular weight polylactic acid products, and the reaction efficiency is much higher than that of the conventional lactic acid dehydration preparation process, greatly improving the polymerization progress of the reaction. degree, increase molecular weight and yield, thereby improving the quality of the final polylactic acid product and overall production efficiency. This application effectively increases the molecular weight of polylactic acid synthesis while reducing costs.

In particular, the polymerization efficiency of PLA prepared from lactic acid ester is higher than that of traditional lactic acid dehydration polymerization. This can not only improve the reaction efficiency but also significantly reduce the production cost of polylactic acid. It is a new industrial production process route with very important significance and broad development prospects.

Detailed ways

In order to be able to understand the technical features and content of the present application in detail, the preferred embodiments of the present application will be described in more detail below. Although the preferred embodiments of the present application are described in the examples, it should be understood that the present application can be implemented in various forms and should not be limited to the embodiments set forth here. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

definition

"Hydrocarbyl" as used herein refers to a monovalent group consisting solely of hydrogen and carbon. Hydrocarbon groups include aliphatic hydrocarbon groups and aromatic hydrocarbon groups, such as alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, cycloalkenyl groups, aryl groups (such as phenyl or benzyl groups), and the like. As used herein, C _x means that there are X carbon atoms in the modified group.

"Heterohydrocarbyl" refers to a hydrocarbyl group in which at least one carbon, but not all carbons, is replaced by a heteroatom.

In this context, heteroatoms may be selected from halogen atoms (fluorine, chlorine, bromine, iodine), phosphorus, nitrogen, sulfur, oxygen, etc.

The "atmospheric pressure" used in this article refers to 1 standard atmospheric pressure, which is approximately 0.1MPa.

As used herein, "polylactic acid" refers to a polyester polymer having a main chain of repeating units with the structure shown below. In this article, the (weight average) molecular weight of polylactic acid is at least 500 (g/mol), and generally can reach more than 1000, that is, the number n of repeating units can be at least 7, and generally can be more than 15. It can be understood that there will be a very small amount of other end groups or linking groups in polylactic acid due to the specific process used, but this does not affect the representation of the main chain structure of polylactic acid.

The inventor of the present application intends to provide a new and improved method for preparing polylactic acid. In the prior art, polylactic acid can generally be prepared by direct polycondensation of lactic acid and ring-opening polycondensation of lactide. However, polylactic acid obtained by the direct (dehydration) condensation polymerization method of lactic acid usually has the disadvantages of low molecular weight and very difficult further dehydration.

Lactic acid esters (such as methyl lactate) are important intermediates in the process of obtaining lactic acid through traditional industrial fermentation. As an important solvent and intermediate raw material in the chemical and pharmaceutical fields, lactate ester is also widely used, such as in medicine, resin coatings, adhesives, cleaning agents, dry cleaning fluids, printing inks and other fields.

The inventor of the present application unexpectedly discovered for the first time that polylactic acid with high molecular weight and high yield can be easily obtained when lactic acid ester is used as a monomer for polycondensation reaction and dealcoholization condensation.

Therefore, according to the present application, a method for manufacturing polylactic acid is provided, which includes subjecting lactic acid ester monomer to a polycondensation reaction to obtain polylactic acid.

In principle, various suitable lactic acid esters can be used in this polycondensation reaction. However, in order to facilitate the polycondensation reaction, lactic acid ester has the following structural formula:

Wherein R represents a substituted or unsubstituted C ₁ -C ₂₀ hydrocarbyl group or a substituted or unsubstituted C ₁ -C ₂₀ heterohydrocarbyl group.

In some embodiments, R is selected from linear or branched C ₁ -C ₂₀ alkyl, linear or branched C ₂ -C ₂₀ alkenyl, linear or branched C ₂ -C ₂₀ alkynyl, C ₃ -C ₂₀ cycloalkyl, C ₃ -C ₂₀ cycloalkenyl, C ₆ -C ₂₀ aryl, C ₃ -C ₂₀ heteroaryl, C ₃ -C ₂₀ heterocycloalkyl, C ₃ -C ₂₀ hetero A group of one of cycloalkenyl and C ₄ -C ₂₀ heteroaralkyl, wherein the group is unsubstituted or selected from C ₁ -C ₁₀ Substituents in alkyl, C ₁ -C ₁₀ alkoxy, C ₃ -C ₁₀ cycloalkyl, mercapto, halogen, cyano, carbonyl or amino are mono- or disubstituted.

In some preferred embodiments, R can be C ₁ -C ₁₂ alkyl, more preferably C ₁ -C ₆ alkyl, particularly preferably C ₁ -C ₄ alkyl, such as methyl, ethyl, propyl, Isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl and its isomers, hexyl and its isomers, heptyl and its isomers, octyl and its isomers, nonyl and its isomers, decyl and its isomers, undecyl and its isomers, dodecyl and its isomers isomer. In a particularly preferred embodiment, R is C ₁ -C ₄ alkyl, especially methyl.

The manufacturing method of polylactic acid according to the present application may directly use lactic acid ester monomers, or may include a step of preparing and obtaining lactic acid ester monomers through an esterification reaction before the polycondensation reaction step. In some embodiments, the lactic acid ester monomer can be prepared from the esterification reaction of lactic acid and a monohydric alcohol represented by ROH. Specifically, R is as defined above. Alternatively, the monohydric alcohol may be selected from methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, cyclohexanemethanol, octanol, nonanol, decanol, undecanol, dodecanol, tetradecanol Alcohol, cetyl alcohol, heptadecanol, stearyl alcohol, cyclopentanol, cyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, 4-methylcyclohexanol, benzyl alcohol, benzene Ethanol, benzyl alcohol, naphthyl alcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, propanol, 3-methoxybutanol, vinyl alcohol , 2-aminoethanol, 2-(ethylamino)ethanol, 2-(dimethylamino)ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, 2-methyl-1-butanol, isopropanol Pentanol, sec-pentanol, 3-pentanol, tert-pentanol, sec-isoamyl alcohol, 4-methyl-2-pentanol, 2-hexanol, 2-ethylbutanol, 2-methylpentanol, 2-Methyl-2-pentanol, 2-methyl-3-pentanol, 3-ethyl-3-pentanol, 2-heptanol, 3-heptanol, 2-octanol, 2-ethylhexanol alcohol, 3,5,5-trimethylhexanol, 2,6-dimethyl-4-heptanol, etc.

In some preferred embodiments, the lactate monomer may be selected from the group consisting of methyl lactate, ethyl lactate, propyl lactate, isopropyl lactate, butyl lactate, isobutyl lactate, sec-butyl lactate, tert-butyl lactate esters, amyl lactate, isoamyl lactate and esters of lactic acid with C ₆ -C ₂₀ monoalcohols. In the method according to the present application, particularly preferred lactate monomers are methyl lactate, ethyl lactate, propyl lactate, isopropyl lactate, butyl lactate, isobutyl lactate, sec-butyl lactate, tert-lactate Butyl ester, amyl lactate, isoamyl lactate. Although this application intends to include all lactic acid esters suitable for polycondensation reactions, it is preferred to use those lactic acid esters that are easy to obtain and preserve for transportation, such as methyl lactate, ethyl lactate, etc., which can significantly reduce the cost of obtaining lactic acid.

It can be understood that the polycondensation reaction of lactic acid ester can be carried out under the action of a catalyst. In principle, various catalysts capable of promoting (ie catalyzing) the polycondensation of lactic acid esters can be used. Specifically, the catalyst used in the polycondensation reaction may include a variety of acidic or basic substances. For example, the catalyst used in the lactic acid ester polycondensation reaction can be selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, carboxylic acid, Lewis acid, acid salt, halide, tin salt, stannous salt, zinc salt, titanium salt, antimony salt, One or more of germanium salts, metal oxides, rare earth compounds, phosphotungstic heteropolyacids, inorganic bases, basic salts, sodium alkyl sulfonates, and organic bases. In some embodiments, preferred catalysts are concentrated sulfuric acid, stannous chloride, and/or stannous octoate.

In the polycondensation reaction of lactic acid ester, the amount of catalyst can be appropriately selected, for example, it can be 0.01 wt% to 50 wt%, based on the amount of lactic acid ester. In some preferred embodiments, the catalyst is used in an amount of 0.5 to 10 wt%, preferably 1 to 5 wt%, based on the amount of lactic acid ester.

In some embodiments, the polycondensation reaction can be carried out at a temperature of 0°C to 350°C, preferably 50°C to 300°C, more preferably 100°C to 250°C, most preferably 100°C to 200°C.

In some preferred embodiments, the polycondensation reaction is carried out at an absolute pressure of 1 Pa to 20 MPa, preferably 10 Pa to 10 MPa, preferably 0.1 kPa to 1 MPa, and more preferably 0.01 MPa to 1 MPa.

In some preferred embodiments, the polycondensation reaction lasts for 0.001 hours to 500 hours, such as 1 hour to 200 hours. Those skilled in the art can adjust the reaction time within an appropriate range as needed.

The inventors of the present application have found that it is advantageous according to the present application that the polycondensation reaction starting from the lactic acid ester monomer is carried out in steps, for example in two steps, three steps or four steps.

For example, the polycondensation reaction may be carried out at a first pressure and a first temperature for a first time, and then may be carried out at a second pressure and a second temperature for a second time after changing the degree of vacuum and/or changing the temperature. Preferably, the polycondensation reaction can also be performed at a third pressure and a third temperature for a third time after changing the degree of vacuum and/or changing the temperature. Here, the absolute pressure in the first step, that is, the first pressure, generally needs to be greater than or equal to atmospheric pressure, for example, it can be from 0.1MPa to 20MPa, for example, from 0.1MPa to 10MPa, or from 0.1MPa to 5MPa. In preferred embodiments, the absolute pressure in the second and subsequent steps, ie the second pressure and the third pressure if present, etc., is generally less than atmospheric pressure, for example from 0.1 kPa to less than 0.1 MPa. In a preferred embodiment, in the second The temperatures in this step and optional subsequent steps, ie the second temperature and if present a third temperature, etc., may be greater than or equal to, preferably greater than, the temperature in the first step, ie the first temperature.

In a further preferred embodiment, the polycondensation reaction is carried out in three steps. At this time, it is advantageous that the absolute pressure in the third step, that is, the third pressure, can be less than or equal to, preferably less than, the absolute pressure in the second step, that is, the second pressure. It is also advantageous that the third temperature can be greater than or equal to, preferably greater than, the second temperature.

Without intending to be bound by theory, the inventors believe that appropriate high pressure in the first step is beneficial to reducing the volatilization loss of monomers, promoting the initiation of the polymerization reaction and initially generating polymers, by subsequently raising the reaction temperature and/or lowering it. Pressure (vacuum) can conveniently promote the discharge of small molecule products of the polycondensation reaction (i.e. monohydric alcohol), thereby further promoting polymerization and thereby increasing the molecular weight of the polymer. In addition, the discharged small molecule product, namely monohydric alcohol, can even be recycled and reused. For example, the discharged monoalcohol can also be recycled to react with lactic acid to produce lactic acid ester, which is obviously very environmentally friendly.

As an alternative optimization step, the product obtained from the reaction can be purified after the polycondensation reaction is completed. Purification can be carried out by methods known in the art.

The weight average molecular weight of the polylactic acid product thus prepared can be at least greater than 500, generally greater than 1000, preferably greater than 2000 or 2500. In a preferred case, the weight average molecular weight of the polylactic acid product thus prepared can even be greater than 10,000.

In order to further increase the molecular weight of the final polylactic acid, the resulting product can be chain extended after the polycondensation reaction. Therefore, this application also provides a manufacturing method of polylactic acid, including the following steps:

a) causing the lactic acid ester monomer to undergo a polycondensation reaction to obtain a polylactic acid prepolymer;

b) Optionally, the polylactic acid prepolymer is subjected to a transesterification reaction with an exchange reagent selected from diols and dicarboxylic acids or their anhydrides, thereby forming an intermediate in which both end groups are hydroxyl or carboxyl groups. bulk polymer; and

c) causing a chain extension reaction between the intermediate polymer and a chain extender to obtain high molecular weight polylactic acid.

In step a), the obtained polylactic acid prepolymer can optionally be purified and used in subsequent steps.

In this method, step a) regarding the "polycondensation reaction" and the purification step and what can be used for the condensation The description of the catalyst for the polymerization reaction is the same as above.

Transesterification is optional. Whether a transesterification step is required depends on the subsequent chain extender used. This transesterification step can be omitted when the chain extender used is, for example, an epoxy resin.

At this time, the manufacturing method of polylactic acid according to the present application may include the following steps:

a’) causing a polycondensation reaction of lactic acid ester monomer to obtain a polylactic acid prepolymer; and

c’) subject the polylactic acid prepolymer to a chain extension reaction with a chain extender selected from epoxy resins, thereby obtaining high molecular weight polylactic acid.

In some embodiments of the method according to the present application, when the transesterification reaction step is adopted, as the transesterification reagent used in the transesterification reaction, the glycol can be selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, and pentanediol. , one or more of hexylene glycol, especially ethylene glycol.

In some embodiments of the method according to the present application, when the transesterification reaction step is adopted, as the transesterification reagent used in the transesterification reaction, the dicarboxylic acid or anhydride thereof is selected from the group consisting of terephthalic acid, phthalic acid, One or more of malonic acid, succinic acid, butenedioic acid, glutaric acid, adipic acid, and suberic acid.

In the step of transesterification reaction, the amount of transesterification agent used is not particularly limited. Generally, the glycol or dicarboxylic acid may be in a slight excess relative to the end groups of the polylactic acid chain. After the reaction, excess diol or dibasic acid can be distilled off.

The transesterification reaction may be carried out at a temperature of greater than 0 to 300°C, such as 100°C to 200°C. The transesterification reaction can be carried out under an appropriate pressure, such as an absolute pressure of 0.1 kPa to 10 MPa. The transesterification reaction time is greater than 0 to 500 hours, for example, 1 to 100 hours. Those skilled in the art can select appropriate temperature, pressure and time for transesterification reaction according to actual needs. If necessary, those skilled in the art can choose to use a catalyst well known in the relevant art or not to use a catalyst in the transesterification reaction according to the selected transesterification reagent to promote the reaction.

After the transesterification reaction is completed, that is, after step b) is completed, a polylactic acid polymer with both terminal groups being hydroxyl or carboxyl groups is obtained, which is also referred to as an intermediate polymer herein.

In a preferred embodiment, in order to further increase the molecular weight of polylactic acid, polylactic acid (herein also referred to as intermediate polymer) can be chain extended. The chain extender may be selected from one or more alcohols or amine compounds or epoxy resins with low molecular weight polyfunctional groups containing hydroxyl or amino groups. For example, the chain extender may be selected from epoxy resins, diisocyanates and/or dioxazolines. Two differences Cyanate chain extenders include, for example, diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), dicyclohexyl diisocyanate (HMDI), isophorone diisocyanate Isocyanate (IPDI). For polylactic acid whose two terminal groups are carboxyl groups after transesterification, oxazoline chain extenders are generally used, while for polylactic acid whose two terminal groups are hydroxyl groups after transesterification, diisocyanate chain extenders are generally used. For epoxy resin chain extenders, the transesterification step can be omitted.

Those skilled in the art can select the amount of chain extender according to needs. Generally speaking, the amount of chain extender should not be excessive relative to the end groups of the polymer, and the amount can be appropriately reduced. The chain extension reaction can be carried out at a temperature of greater than 0°C to 300°C, such as 100°C to 200°C. The chain extension reaction can be carried out at a pressure of 0.1kPa-10MPa. The chain extension reaction is carried out for greater than 0 to 500 hours, such as 1 to 100 hours. Those skilled in the art can select appropriate temperature, pressure and time for the chain extension reaction according to actual needs. If necessary, those skilled in the art can choose to use a catalyst well known in the relevant art or not to use a catalyst in the chain extension reaction according to the selected chain extender to promote the reaction.

After the chain extension reaction is completed, that is, after step c), the molecular weight of the intermediate polymer can be effectively increased. The weight average molecular weight of the polylactic acid thus prepared can be greater than 5,000, even greater than 10,000, preferably greater than 50,000.

Therefore, this application also provides polylactic acid prepared according to the above method.

The advantages of preparing polylactic acid according to the preparation method of the present application will be further confirmed below with reference to specific examples.

Example

The raw materials and catalysts used in each embodiment can be obtained from the market or directly obtained according to general synthesis methods. In addition, unless otherwise specified in each example, the reaction pressure used is approximately atmospheric pressure.

For the convenience of explanation, methyl lactate is used as an example to illustrate the synthesis route of polylactic acid in each embodiment, which can be seen in the following formula:

Step a)

Step b): transesterification reaction:

Step c): Chain extension reaction:

Example 1

Put 150g ethyl lactate and 3wt% concentrated sulfuric acid (98%) into a stirred reaction kettle, and react under 0.5MPa pressure and 170°C for 25 hours to obtain polylactic acid with a weight average molecular weight of 1539 and a yield of 92% .

Example 2

Put 150g butyl lactate and 5wt% concentrated sulfuric acid (98%) into a stirred reaction kettle with reflux, and react at atmospheric pressure and 160-180°C for 18 hours to obtain polylactic acid with a weight average molecular weight of 1735, yield is 86%.

Example 3

Put 50g methyl lactate and 2.5wt% concentrated sulfuric acid (98%) into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 16 hours to obtain polylactic acid with a weight average molecular weight of 563 and a yield of 79.86%.

Example 4

Put 150g isoamyl lactate and 1wt% concentrated sulfuric acid (98%) into a stirred reaction kettle with reflux, and react at atmospheric pressure and 160-175°C for 32 hours to obtain polylactic acid with a weight average molecular weight of 723. The rate is 94.5%.

Example 5

Put 50g methyl lactate and 2.5wt% concentrated sulfuric acid (98%) into a stirrer with reflux In the reaction kettle, react at 0.2MPa pressure and 140°C for 16 hours to obtain polylactic acid prepolymer.

Then change the pressure, set the temperature to 140°C, and evacuate for 4 hours with a vacuum degree of 0.05-0.09MPa to obtain polylactic acid with a weight average molecular weight of 1750 and a yield of 69.6%.

Example 6

Put 50g methyl lactate and 2.5wt% concentrated sulfuric acid (98%) into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then the pressure was changed, the temperature was 140°C, and the vacuum was evacuated for 4 hours with a vacuum degree of 0.05-0.09MPa to obtain polylactic acid with a weight average molecular weight of 2350 and a yield of 73.23%.

Example 7

Put 50g methyl lactate and 2.5wt% concentrated sulfuric acid (98%) into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 16 hours to obtain a polylactic acid prepolymer.

Then change the pressure, set the temperature to 140°C, and evacuate for 4 hours with a vacuum degree of 0.05-0.09MPa to obtain the first polymer.

Add ethylene glycol to the first polymer obtained in the above step, and conduct transesterification reaction at 140° C. for 4 hours to obtain a transesterification product.

MDI was added to the transesterification product obtained in the above step, and chain extension reaction was performed at 160°C for 1 hour to obtain a polylactic acid product with a weight average molecular weight of 7079 and a yield of 72.54%.

Example 8

Put 50g methyl lactate and 2.5wt% concentrated sulfuric acid (98%) into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C for 4 hours and a vacuum degree of 0.05-0.09MPa to obtain the first polymer.

Then, ethylene glycol was added, and the transesterification reaction was performed at 140°C for 4 hours to obtain the transesterification product.

MDI was added to the transesterification product obtained in the above step, and chain extension reaction was performed at 160°C for 1 hour to obtain a polylactic acid product with a weight average molecular weight of 9054 and a yield of 72.27%.

Example 9

Put 100g of ethyl lactate and 2.5wt% stannous chloride into a stirred reaction kettle with reflux, and react at atmospheric pressure and 150°C for 32 hours to obtain a polylactic acid prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C for 24 hours to obtain a polymer. The polylactic acid product was obtained with a weight average molecular weight of 2052 and a yield of 71.17%.

Example 10

Put 100g of methyl lactate and 2.5wt% stannous chloride into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then, vacuum at a degree of 0.05-0.09MPa and a temperature of 140°C for 12 hours to obtain a polymer with a weight average molecular weight of 1326 and a yield of 58.26%.

Example 11

Put 100g of methyl lactate and 2.5wt% stannous chloride into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C for 12 hours to obtain the first polymer.

The temperature of the first polymer obtained in the above step was raised to 170° C., and the polymer was evacuated at a vacuum degree of 0.05-0.09 MPa for 12 hours to obtain a polymer with a weight average molecular weight of 2357 and a yield of 59.74%.

Example 12

Put 100g of methyl lactate and 2.5wt% stannous chloride into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C for 12 hours to obtain the first polymer.

The temperature of the first polymer obtained in the above step was raised to 170°C, and vacuum was applied at 0.05-0.09MPa for 24 hours to obtain a polylactic acid polymer with a weight average molecular weight of 2861 and a yield of 56.65%.

Example 13

Put 100g methyl lactate and 2.5wt% stannous chloride into a stirred reaction with reflux In the kettle, react at atmospheric pressure and 140°C for 32 hours to obtain polylactic acid prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140-155°C for 36 hours to obtain the first polymer.

The temperature of the first polymer obtained in the above steps was raised to 170-180°C, and vacuum was evacuated at a vacuum degree of 0.09-0.095 MPa for 48 hours to obtain a polymer with a weight average molecular weight of 5633 and a yield of 59%.

Example 14

Put 100g of methyl lactate and 2.5wt% stannous chloride into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140-160°C for 48 hours to obtain the first polymer.

The temperature of the first polymer obtained in the above steps was raised to 170-185°C, and vacuum was evacuated at a vacuum degree of 0.09-0.096MPa for 96 hours to obtain a polymer with a weight average molecular weight of 10366 and a yield of 59.5%.

Example 15

Put 100g of methyl lactate and 2.5wt% stannous octoate into a stirred reaction kettle with reflux, and incubate at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then, at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C, vacuum was evacuated for 4 hours to obtain a polymer with a weight average molecular weight of 863 and a yield of 65.56%.

Example 16

Put 100g of methyl lactate and 2.5wt% stannous octoate into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then, at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C, vacuum was applied for 12 hours to obtain a polymer with a weight average molecular weight of 1033 and a yield of 62.1%.

Example 17

Put 50g ethyl lactate and 2.5wt% stannous octoate into a stirred reaction kettle with reflux , and reacted at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C for 12 hours to obtain the first polymer.

Then the temperature was raised to 170°C, and vacuum was evacuated at a vacuum degree of 0.05-0.09MPa for 12 hours to obtain a polymer with a weight average molecular weight of 1689 and a yield of 63%.

Example 18

Put 50g of methyl lactate and 2.5wt% stannous octoate into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C for 12 hours to obtain the first polymer.

Then the temperature was raised to 170°C, and vacuum was evacuated at a vacuum degree of 0.05-0.09MPa for 24 hours to obtain a polymer with a weight average molecular weight of 2045 and a yield of 62%.

Example 19

Put 50g of methyl lactate and 2.5wt% stannous octoate into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C for 12 hours to obtain the first polymer.

Then the temperature was raised to 170°C, and vacuum was evacuated at a vacuum degree of 0.05-0.09MPa for 36 hours to obtain a polymer with a weight average molecular weight of 2257 and a yield of 61%.

Example 20

Put 50g of methyl lactate and 2.5wt% stannous octoate into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

Then, vacuum at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C for 12 hours to obtain the first polymer.

Then the temperature was raised to 170°C, and vacuum was evacuated at a vacuum degree of 0.05-0.09MPa for 48 hours to obtain a polymer with a weight average molecular weight of 3251 and a yield of 60%.

Example 21

Put 100g methyl lactate, 1wt% stannous octoate and 3.5wt% stannous chloride into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

At a vacuum degree of 0.05-0.09MPa and a temperature of 140-150°C, vacuum for 22 hours. Then the temperature is raised to 170-185°C, and the first polymer is obtained by vacuuming for 80 hours at a vacuum degree of 0.09-0.096MPa.

Add ethylene glycol to the first polymer obtained in the above step, and conduct transesterification reaction at 140° C. for 4 hours to obtain a transesterification product.

MDI was added in portions to the transesterification product obtained in the above step, and chain extension reaction was carried out at 160°C for 2 hours to obtain a polylactic acid product with a weight average molecular weight of 50224 and a yield of 58.1%.

Example 22

Put 100g of methyl lactate and 2wt% stannous chloride into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Then, evacuate for 20 hours at a vacuum degree of 0.05-0.09MPa and a temperature of 140°C, then increase the temperature to 170-180°C and evacuate for 48 hours at a vacuum degree of 0.09-0.095MPa to obtain the first polymer.

Add ethylene glycol to the first polymer obtained in the above step, and conduct transesterification reaction at 140-170°C for 4 hours to obtain a transesterification product.

MDI was added to the transesterification product obtained in the above step, and chain extension reaction was carried out at 160-170°C for 1 hour to obtain a polylactic acid product with a weight average molecular weight of 15254 and a yield of 55.7%.

Example 23

Put 100g of methyl lactate and 3wt% stannous chloride into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a polylactic acid prepolymer.

Add 0.05-0.09MPa vacuum to the prepolymer obtained in the prepolymerization step, vacuum for 20 hours at a temperature of 140-160°C, increase the temperature to 170-185°C, and vacuum for 72 hours at a vacuum of 0.09-0.095MPa The first polymer is obtained.

Add ethylene glycol to the first polymer obtained in the above step, and conduct transesterification reaction at 140 to 170° C. for 4 hours to obtain a transesterification product.

MDI was added to the transesterification product obtained in the above step, and chain extension reaction was carried out at 160-180°C for 2 hours to obtain a polylactic acid product with a weight average molecular weight of 40224 and a yield of 58.1%.

Example 24

Put 100g methyl lactate, 2wt% zinc oxide (98%) and 2% p-toluenesulfonic acid into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

Add 0.05-0.09MPa vacuum to the prepolymer obtained in the prepolymerization step, vacuum for 24 hours at a temperature of 140-150°C, increase the temperature to 170-180°C, and vacuum for 72 hours at a vacuum of 0.09-0.096MPa The first polymer is obtained.

Add ethylene glycol to the first polymer obtained in the above step, and conduct transesterification reaction at 140 to 150° C. for 4 hours to obtain a transesterification product.

MDI was added in portions to the transesterification product obtained in the above step, and chain extension reaction was carried out at 140-160°C for 1 hour to obtain a polylactic acid product with a weight average molecular weight of 30,381 and a yield of 56%.

Example 25

Put 100g methyl lactate and 4wt% stannous chloride (98%) into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 48 hours to obtain a polylactic acid prepolymer.

Then, evacuate for 56 hours at a vacuum degree of 0.05-0.09MPa and a temperature of 140-160°C, then increase the temperature to 170-190°C and evacuate for 96 hours at a vacuum degree of 0.09-0.098MPa to obtain the first polymer.

Add ethylene glycol to the first polymer obtained in the above step, and conduct transesterification reaction at 140-170°C for 6 hours to obtain a transesterification product.

MDI was added to the transesterification product obtained in the above step, and chain extension reaction was carried out at 160-190°C for 3 hours to obtain a polylactic acid product with a weight average molecular weight of 76562 and a yield of 57.9%.

Example 26

Put 100g methyl lactate and 5wt% stannous chloride (98%) into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 48 hours to obtain a polylactic acid prepolymer.

Then vacuum at a vacuum degree of 0.095MPa and a temperature of 140 to 165°C for 72 hours. Raise the temperature to 170-195°C and evacuate at a vacuum degree of 0.09-0.099MPa for 120 hours to obtain the first polymer.

Ethylene glycol is added to the first polymer obtained in the above step, and transesterification reaction is carried out at 140 to 170° C. for 8 hours to obtain a transesterification product.

Add MDI to the transesterification product obtained in the above step, and perform a chain extension reaction at 160 to 190°C for 5 hours to obtain a polylactic acid product with a weight average molecular weight of 106852 and a yield of 59%.

Example 27

Put 100g of methyl lactate and 3.5wt% stannous chloride into a reactor with reflux stirring, and react at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

Add 0.05-0.09MPa vacuum degree to the prepolymer obtained in the above step, set the temperature to 140-150°C, and evacuate for 40 hours to obtain the first polymer.

Then the temperature was raised to 160-180°C, and vacuum was evacuated at a vacuum degree of 0.09-0.096MPa for 92 hours to obtain a polymer with a weight average molecular weight of 13272 and a yield of 58%.

Example 28

Put 100g of methyl lactate, 3.5wt% stannous chloride and 1.5% p-toluenesulfonic acid into a stirred reaction kettle with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

Add 0.05-0.09MPa vacuum degree to the prepolymer obtained in the above step, set the temperature to 140-160°C, and evacuate for 50 hours to obtain the first polymer.

Then the temperature was raised to 160-180°C, and vacuum was evacuated at a vacuum degree of 0.09-0.098MPa for 96 hours to obtain a polymer with a weight average molecular weight of 20596 and a yield of 57%.

Example 29

Put 100g of methyl lactate and 2.5wt% stannous chloride into a stirred reactor with reflux, and react at atmospheric pressure and 140°C for 32 hours to obtain a prepolymer.

Add a vacuum degree of 0.05-0.09MPa to the prepolymer obtained in the above step, and vacuum for 12 hours at a temperature of 140°C to obtain the first polymer.

Then increase the temperature to 165-175°C and vacuum for 72 hours at a vacuum degree of 0.05-0.09MPa. When, a polymer was obtained with a weight average molecular weight of 3809 and a yield of 57.9%.

The embodiments of the present application have been described above. The above description is illustrative, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the present application.

Claims (10)

1. The manufacturing method of polylactic acid includes subjecting lactic acid ester monomer to undergo a polycondensation reaction to obtain polylactic acid.
2. The manufacturing method of polylactic acid includes:

   a) subjecting the lactic acid ester monomer to a polycondensation reaction to obtain a polylactic acid prepolymer, and optionally, purifying the polylactic acid prepolymer;

   b) Optionally, the polylactic acid prepolymer is subjected to a transesterification reaction with an exchange reagent selected from any one of diols and dicarboxylic acids or anhydrides thereof, thereby forming a polylactic acid prepolymer with both end groups being hydroxyl or carboxyl groups. intermediate polymers; and

   c) causing a chain extension reaction between the intermediate polymer and a chain extender to obtain high molecular weight polylactic acid.
3. The method according to claim 1 or 2, wherein the lactic acid ester monomer has the following structural formula:
   

   wherein R represents a substituted or unsubstituted C ₁ -C ₂₀ hydrocarbyl group or a substituted or unsubstituted C ₁ -C ₂₀ heterohydrocarbyl group;

   Preferably, R is selected from linear or branched C ₁ -C ₂₀ alkyl, linear or branched C ₂ -C ₂₀ alkenyl, linear or branched C ₂ -C ₂₀ alkynyl, C ₃ -C ₂₀ cycloalkyl, C ₃ -C ₂₀ cycloalkenyl, C ₆ -C ₂₀ aryl, C ₃ -C ₂₀ heteroaryl, C ₃ -C ₂₀ heterocycloalkyl, C ₃ -C ₂₀ heterocycloalkenyl , a group of one of C ₄ -C ₂₀ heteroaralkyl, wherein the group is unsubstituted or selected from C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ alkoxy, C ₃ - The substituents in C ₁₀ cycloalkyl, mercapto, halogen, cyano, carbonyl or amino are mono- or disubstituted;

   More preferably, R is a C ₁ -C ₂₀ alkyl group, more preferably a C ₁ -C ₁₂ alkyl group, even more preferably a C ₁ -C ₆ alkyl group, particularly preferably a C ₁ -C ₄ alkyl group, such as methyl, ethyl base, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl and its isomers, hexyl and its isomers, heptyl and its isomers Formation, octyl and its isomers, nonyl and its isomers body, decyl and its isomers, undecyl and its isomers, dodecyl and its isomers.
4. The method of claim 3, wherein the lactic acid ester monomer is formed from lactic acid and a monohydric alcohol represented by ROH, wherein R is as defined in claim 3; or

   The lactate monomer is selected from the group consisting of methyl lactate, ethyl lactate, propyl lactate, isopropyl lactate, butyl lactate, isobutyl lactate, sec-butyl lactate, tert-butyl lactate, amyl lactate, lactic acid One or more of isopentyl esters and esters of lactic acid and C ₆ -C ₂₀ monoalcohols.
5. The method according to claim 1 or 2, wherein,

   The polycondensation reaction is carried out under the action of a catalyst, wherein the catalyst is an acidic or alkaline substance, preferably selected from sulfuric acid, hydrochloric acid, phosphoric acid, carboxylic acid, Lewis acid, acid salt, halide, tin salt, stannous salt , one or more of zinc salts, titanium salts, antimony salts, germanium salts, metal oxides, rare earth compounds, phosphotungstic heteropoly acids, inorganic bases, basic salts, sodium alkyl sulfonates, and organic bases, preferably fatty acids stannous and stannous chloride;

   Optionally, the catalyst is used in an amount of 0.01 to 50 wt% based on the amount of lactic acid ester, preferably 0.5 to 10 wt%, more preferably 1 to 5 wt%.
6. The method according to claim 1 or 2, wherein the polycondensation reaction is carried out at a temperature of 0°C to 350°C, preferably 50°C to 300°C, more preferably 100°C to 250°C, most preferably 100°C to 200°C, and / Or at an absolute pressure of 1 Pa to 20 MPa, preferably 10 Pa to 10 MPa, more preferably 0.1 kPa to 1 MPa, for 0.001 hours to 500 hours, for example, 1 hour to 200 hours.
7. The method according to claim 1 or 2, wherein the polycondensation reaction is carried out in steps, such as two steps, three steps or four steps, wherein the absolute pressure in the first step is greater than or equal to atmospheric pressure, for example from 0.1MPa to 20MPa, the absolute pressure in the second step and optional subsequent steps is less than atmospheric pressure, for example from 0.1kPa to less than 0.1MPa, and/or the temperature in the second step and optional subsequent steps is greater than or equal to the first step temperature;

   Preferably, the polycondensation reaction is carried out in three steps, wherein the absolute pressure of the third step is less than or equal to, preferably less than the absolute pressure of the second step, and/or the temperature in the third step is greater than or equal to, preferably greater than the temperature in the second step. .
8. The method of claim 2, wherein the transesterification reaction is carried out at a temperature greater than 0 to 300°C, such as 100°C to 200°C, for 0.01 hours to 500 hours, such as 1 hour to 100 hours; and/or

   The glycol is one or more selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, pentanediol and hexylene glycol; and/or

   The dicarboxylic acid is one or more selected from the group consisting of terephthalic acid, phthalic acid, malonic acid, succinic acid, butenedioic acid, glutaric acid, adipic acid and suberic acid. .
9. The method of claim 2, wherein the chain extender is one or more selected from the group consisting of low molecular weight polyfunctional alcohols or amine compounds containing hydroxyl or amino groups and epoxy resins, preferably selected from the group consisting of Diisocyanate, dioxazoline, epoxy resin, among which diisocyanate chain extenders include diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), bicyclic Hexyl diisocyanate (HMDI), isophorone diisocyanate (IPDI); and/or

   The chain extension reaction is carried out at a temperature of greater than 0 to 300°C, such as 100°C to 200°C, for 0.01 to 500 hours, such as 1 to 100 hours.
10. The polylactic acid produced by the method of any one of claims 1 to 9 preferably has a weight average molecular weight greater than 500; or a weight average molecular weight greater than or equal to 1,000; or a weight average molecular weight greater than 2,000; or a weight average molecular weight greater than 5000; or the weight average molecular weight is greater than 10000, or the weight average molecular weight is greater than 50000.