A macrocyclic (ketal-ester) monomer and chemically recyclable poly(ketal-ester) and methods of synthesis thereof

Abstract

The application discloses a kind of macrocycle (ketal-ester) monomer and chemically recyclable poly (ketal-ester) and its synthesis method, based on the compound of the structure of bio-based raw material 4-ketocarboxylic acid and 1,1,1-trihydroxy methyl compound, by one-pot dehydration condensation synthesis eighteen-membered dimer macrocycle (ketal-ester).The macrocycle (ketal-ester) is synthesized by ring-opening polymerization and ring-opening copolymerization a series of novel poly (ketal-ester) materials with novel properties.This kind of poly (ketal-ester) can be polymerized at industrial production temperature, can be hot processed into shape without strictly removing catalyst, material performance can be adjusted and monomer recycling can be realized under mild conditions, and is expected to be applied on a large scale, become a new generation of green polymer materials.

Description

Technical Field

[0001] This invention relates to methods for synthesizing macrocyclic (ketal-ester) and poly(ketal-ester), specifically to a method for synthesizing an 18-membered macrocyclic (ketal-ester) and its ring-opening polymerization and ring-opening copolymerization to synthesize chemically recyclable poly(ketal-ester), belonging to the field of polymer material synthesis. Background Technology

[0002] Over a century of development in polymer science has spurred the rapid advancement of the polymer industry, resulting in the creation of countless high-performance synthetic polymer materials widely applied in all aspects of modern society, greatly contributing to human civilization and improving the quality of life. Currently, widely used general-purpose polymer materials include plastics such as polyethylene, polypropylene, polyvinyl chloride, and polystyrene. However, the vast majority of plastics are discarded or landfilled after a single use, and their non-degradability and low recycling rate lead to serious resource waste and environmental pollution. Therefore, utilizing biomass raw materials to innovate novel polymer materials with chemical recyclability and reusability is an important approach to solving this problem and aligns with the concept of sustainable social development. Chemically recycled monomers refer to the depolymerization of used polymers through chemical methods to regenerate monomers. These monomers can then be repolymerized to obtain polymer materials with identical properties. This strategy maintains the performance of polymer materials while significantly reducing dependence on petrochemical resources and decreasing the generation of plastic waste.

[0003] Polymers that can be chemically recycled to monomers are typically synthesized through ring-opening polymerization of cyclic monomers. Aliphatic polyesters have attracted widespread attention due to their excellent and tunable degradability and material properties. Ring-opening polymerization of cyclic ester monomers is an important method for preparing polyesters, and the resulting polyesters have the potential to depolymerize back to monomers under controlled conditions, making them a promising new type of recyclable plastic. The key to achieving this goal lies in rational monomer design, simple and efficient monomer synthesis methods, controlled polymerization under mild conditions, and a balance between material thermal stability, overall performance, and depolymerization ability. The structural design of cyclic ester monomers and polymers is based on polymerization thermodynamics. Specifically, the enthalpy change of the ring-opening polymerization reaction of cyclic esters with higher strain is negative. Entropy becomes negative Under standard conditions, according to the Gibbs free energy equation, there exists a state of equilibrium between polymerization and depolymerization (ΔG). pThe temperature at which polymerization reaches its upper limit (=0) is called the polymerization upper limit temperature. From a chemical equilibrium perspective, lower temperatures favor polymerization, while higher temperatures favor depolymerization. Therefore, monomer recovery can be achieved by increasing the temperature in the presence of a catalyst. The most representative example is the ring-opening polymerization of bio-based γ-butyrolactone reported by Hong and Chen in 2016, which prepared chemically recyclable polyγ-butyrolactone. Polyγ-butyrolactone is stable in the absence of a catalyst, and in the presence of a catalyst, it can depolymerize completely back to γ-butyrolactone at high temperatures. In recent years, a large number of chemically recyclable polymers designed based on the polymerization upper limit temperature have been reported. However, three inherent problems arising from this design strategy have not been simultaneously resolved: First, to achieve high-conversion polymerization of monomers, the polymerization reaction needs to be carried out at extremely low temperatures (e.g., ring-opening polymerization of γ-butyrolactone at -40°C), which is unsuitable for industrial production and significantly increases production energy consumption; second, when a catalyst is present, the polymer material undergoes thermal decomposition, limiting its thermal processing. Strict purification to remove residual catalysts or end-capping of the polymer is required before processing, increasing production costs; third, monomer recovery typically requires high temperatures and vacuum environments, and purification of monomers through vacuum distillation reduces recovery efficiency and increases recovery energy consumption and costs. Furthermore, from the perspectives of production, processing, and use, an ideal polymerizable monomer should be efficiently synthesized and purified from bio-based raw materials; an ideal polymerization process should be easily implemented on a large scale in industrial production to obtain high molecular weight polymers; and an ideal polymer material should possess excellent and tunable material properties, allowing for thermal processing without additional end-capping or strict catalyst removal, and meeting the needs of different application scenarios. Therefore, how to design polymer materials derived from bio-based raw materials, which can be polymerized at industrial production temperatures to obtain high molecular weight polymers, which can be directly thermally processed, have excellent material properties, and can achieve monomer recovery under mild conditions has become a key issue of concern for researchers. Summary of the Invention

[0004] The purpose of this invention is to provide a method for synthesizing macrocyclic (ketal-ester) polymers based on bio-based raw materials, and to establish a method for preparing chemically recyclable poly(ketal-ester) polymers through their ring-opening polymerization. This method ensures that the monomers are polymerized at industrial production temperatures to obtain high molecular weight polymers, which can be thermally processed without strict catalyst removal. This provides a novel type of polymer material with adjustable properties and monomer recovery under mild conditions.

[0005] The technical concept of this invention is that the enthalpy change of the ring-opening polymerization reaction of macrolides is positive. Entropy becomes positive According to the Gibbs free energy equation, there exists a lower limit temperature for polymerization. By rationally designing the macrocyclic lactone structure to possess a suitable lower limit temperature for polymerization, it is possible to polymerize the monomer at relatively high temperatures in industrial production to obtain high molecular weight polymers. In the presence of a catalyst, the polymer can be recycled back to the monomer under mild conditions through ring closure.

[0006] Compounds with a 4-ketocarboxylic acid structure, such as levulinic acid, can be derived from cellulose or sugars and are important biomass raw materials. Utilizing the rich reactivity of the carbonyl and carboxyl bifunctional groups, both skeletal derivatization and esterification reactions can be used to prepare various polymers from keto acids as bifunctional monomers. Compounds with a 1,1,1-tris(hydroxymethyl) structure are diverse; for example, 1,1,1-tris(hydroxymethyl)ethane, 1,1,1-tris(hydroxymethyl)propane, 1,1,1-tris(hydroxymethyl)nitromethane, and 1,1,1-tris(hydroxymethyl)aminomethane are all commercially available raw materials. 1,1,1-tris(hydroxymethyl) compounds can be synthesized using various synthetic methods, compatible with different functional groups. For example, the cannizaro reaction synthesizes 1,1,1-tris(hydroxymethyl)ethane, and nucleophilic addition reactions synthesize 1,1,1-tris(hydroxymethyl)nitromethane. Therefore, compounds with a 1,1,1-tris(hydroxymethyl) structure are characterized by simple synthesis and easy derivatization. 1,1,1-Tris(hydroxymethyl) compounds can undergo simultaneous ketalization and esterification reactions with 4-ketocarboxylic acid compounds under acid catalysis, generating a six-membered ketal ring and an ester bond. By controlling the concentration and solvent, the dehydration reaction can be made more intramolecular, i.e., reacting two molecules of a 1,1,1-tris(hydroxymethyl) compound with two molecules of a 4-ketocarboxylic acid compound to yield an 18-membered ring dimer macrocycle (ketal-ester), such as... Figure 1As shown, the obtained macrocyclic (ketal-ester) can undergo ring-opening polymerization at high temperature under the catalysis of transesterification catalyst to obtain poly(ketal-ester) with different substituent structures. From a processing perspective, this type of poly(ketal-ester) does not undergo cyclization degradation during thermal processing, eliminating the need to remove the catalyst. Therefore, the polymer melt after polymerization can be directly processed without purification. From a material properties perspective, different substituent structures will affect the material properties of poly(ketal-ester), enabling the control of mechanical properties. Furthermore, since the polymerization mechanism of macrocyclic (ketal-ester) is transesterification, macrocyclic (ketal-ester) can also copolymerize with other macrocyclic lactones, and the properties of the polymer can be further controlled by adjusting the copolymerization ratio. From a material recycling perspective, below the lower limit of polymerization temperature, macrocyclic (ketal-ester) is in a more thermodynamically stable state than poly(ketal-ester). Therefore, after the poly(ketal-ester) material is discarded, adding a suitable catalyst can cyclize it back to the macrocyclic (ketal-ester) monomer under mild conditions (e.g., room temperature). The recovered macrocyclic (ketal-ester) compounds can be re-ring-opened and polymerized to obtain poly(ketal-ester) materials with identical properties. Therefore, these poly(ketal-ester) materials are green polymers that can be recycled indefinitely. Examples of compounds with the 4-ketocarboxylic acid structure, compounds with the 1,1,1-tris(hydroxymethyl) structure, and macrocyclic lactones are provided below. Figure 2 .

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a one-pot dehydration condensation synthesis method for macrocyclic (ketal-ester) compounds, comprising: adding an acid catalyst to a mixed organic solution of a 4-ketocarboxylic acid compound of Formula I and a 1,1,1-trihydroxymethyl compound of Formula II, heating to carry out esterification and ketalization reactions, and dehydration cyclization to synthesize a macrocyclic (ketal-ester) compound of Formula III, the reaction formula of which is shown below:

[0009]

[0010] Among them, R 1 Represents one or more substituents, selected from H, alkyl, substituted alkyl, halogen, alkoxy, aryl, etc.; R 2 Represents one or more substituents, selected from H, alkyl, substituted alkyl, halogen, alkoxy, aryl, etc.; R 3 Represents one or more substituents, selected from H, alkyl, substituted alkyl, halogen, alkoxy, aryl, etc.; R 4 Selected from H, alkyl, substituted alkyl, alkenyl, alkynyl, halogen, nitro, amide, alkoxy, aryl, etc.

[0011] The aforementioned halogens include fluorine, chlorine, bromine, and iodine; the aforementioned alkyl groups are preferably C1-C20 alkyl groups, more preferably C1-C6 alkyl groups; the aforementioned substituted alkyl groups have one or more substituents, which are selected from alkenyl, alkynyl, halogen, amide, alkoxy, cyano, aryl, etc.; the aforementioned alkenyl groups are preferably C2-C20 alkenyl groups, more preferably C2-C6 alkenyl groups; the aforementioned alkynyl groups are preferably C2-C20 alkynyl groups, more preferably C2-C6 alkynyl groups; the aforementioned amide groups are preferably C2-C20 amide groups, more preferably C1-C6 amide groups; the aforementioned alkoxy groups are preferably C2-C20 alkoxy groups, more preferably C1-C6 alkoxy groups; the aforementioned aryl groups are preferably C6-C12 aryl groups, such as phenyl.

[0012] Among them, the 4-ketocarboxylic acid structure compound represented by Formula I includes, but is not limited to, levulinic acid, and the 1,1,1-tris(hydroxymethyl) structure compound represented by Formula II includes, but is not limited to, 1,1,1-tris(hydroxymethyl)ethane. Taking the dehydration cyclization of levulinic acid and 1,1,1-tris(hydroxymethyl)ethane to synthesize the macrocyclic compound of Formula IV (ketal-ester) (hereinafter referred to as HOD) as an example, the reaction formula is as follows:

[0013]

[0014] Furthermore, the dehydration cyclization is carried out using an acid catalyst, such as p-toluenesulfonic acid, sulfuric acid, phosphoric acid, etc., which are commercially available reagents and require no special treatment; p-toluenesulfonic acid is preferred. The catalytic amount of the acid catalyst is based on a molar ratio of 0.1% to 10% of the compound shown in Formula I.

[0015] Furthermore, the dehydration cyclization reaction is selected from commercially available organic solvents such as toluene, xylene, n-hexane, and cyclohexane, which are commercially available reagents and require no special treatment; preferably, a mixed solution of toluene and cyclohexane in a volume ratio of 1:1 is used. In some embodiments of the present invention, the concentration of the two reactants in the mixed solution of toluene and cyclohexane is 0.5 mol / L (not limited thereto).

[0016] Furthermore, the amount of compound II is preferably 80% to 120% molar ratio of compound I (but not limited thereto). Water produced by the reaction is removed by azeotropic reaction at a temperature range of 100°C to 140°C, preferably 120°C, and a Dean-Steak water separator is installed to collect the produced water; at the same time, to ensure that the dehydration reaction proceeds fully, the reaction time should be longer than 8 hours.

[0017] Further, the post-reaction treatment includes rotary evaporation, washing, filtration, and drying. The solvents used in the washing process are selected from dichloromethane, chloroform, ethyl acetate, acetone, tetrahydrofuran, anhydrous methanol, diethyl ether, and saturated alkane solvents, such as n-pentane, n-hexane, and cyclohexane. These are commercially available reagents and require no special treatment. Acetone and dichloromethane are preferred as washing solvents. In some embodiments of the present invention, the washing-filtration operation is repeated three times at a ratio of 15 mL of washing solvent per 10 g of crude product (not limited to this). The white powder or colorless crystals obtained after washing and filtration are placed overnight in a vacuum oven at 20–50°C to remove residual solvent, completing the drying process.

[0018] Secondly, the present invention provides a method for synthesizing poly(ketal-ester) poly(ketal-ester) by ring-opening polymerization of macrocyclic (ketal-ester) monomers, comprising: using the macrocyclic (ketal-ester) represented by Formula III as a monomer, and initiating an entropy-driven ring-opening polymerization reaction under high temperature conditions using an ester exchange catalyst in the presence of an initiator, as shown below:

[0019]

[0020] Where n represents the degree of polymerization, which is determined by the molecular weight of the polymer. The preferred polymer should have a molecular weight greater than 20 kDa.

[0021] Taking the ring-opening polymerization of HOD to synthesize the corresponding polymer (hereinafter referred to as PHOD) as an example, the polymerization reaction equation is as follows:

[0022]

[0023] Further, the initiator includes, but is not limited to, alcohol initiators such as ethanol, isopropanol, and benzyl alcohol. The transesterification catalyst includes, but is not limited to, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), stannous octoate, stannous isooctanoate, titanate, etc., which are commercially available reagents and do not require special treatment. A titanate catalyst is preferred, with the general chemical formula Ti(OR')4, where R' is an alkyl group, such as tetraisopropyl titanate (Ti(Oi-Pr)4) and tetrabutyl titanate (Ti(On-Bu)4). When using a titanate catalyst for ring-opening polymerization, the titanate catalyst can also act as an initiator, eliminating the need for additional initiator addition. The catalytic dosage of the catalyst is 0.01% to 10% molar ratio based on the macrocyclic (ketal-ester) monomer.

[0024] Furthermore, polymerization is carried out under bulk or solution conditions. The polymerization solvent is a solvent with a boiling point above 100°C, selected from toluene, xylene, chlorobenzene, dichlorobenzene, trichlorobenzene, diphenyl ether, etc., with chlorobenzene being preferred. To ensure that the polymerization reaction occurs under anhydrous conditions, all solvents are refluxed with metallic sodium to remove water before use, stored under a nitrogen atmosphere, and supplemented with... Molecular sieve.

[0025] Furthermore, the polymerization reaction occurs under anaerobic conditions, using a sealed tube in an inert atmosphere (such as nitrogen). Since the ring-opening polymerization of macrocyclic (ketal-ester) compounds is driven by entropy increase, the reaction temperature should be high, ranging from 80℃ to 260℃, preferably 120℃ to 200℃. The reaction time is determined by the amount of catalyst and the reaction temperature; to ensure high monomer conversion, the reaction time should be between 10 minutes and 24 hours. Taking ring-opening polymerization at 170℃ in a 3 mol / L chlorobenzene solution with a catalyst dosage of 0.5% of the monomer as an example, the preferred reaction time is 6 hours, and the monomer conversion rate is greater than 90%.

[0026] Furthermore, the crude product after polymerization is subjected to vacuum heating to remove the solvent and sublimation to remove unreacted macrocyclic rings (ketals-esters). The vacuum degree is in the range of 5 Pa to 200 Pa, the heating temperature is 170 °C to 260 °C, and the heating time is 30 minutes to 120 minutes.

[0027] Furthermore, to obtain high-purity polymers for characterization, post-treatment of the polymer can be performed, including precipitation and drying. The unsuitable solvents used in the precipitation process are selected from anhydrous methanol, diethyl ether, and saturated alkane solvents (such as n-pentane, n-hexane, cyclohexane, etc.), with anhydrous methanol being preferred as the precipitation solvent. Precipitation and centrifugation are carried out at room temperature. The polymer is then placed overnight in a vacuum oven at 20–50°C to remove residual solvent and complete the drying process.

[0028] Thirdly, the present invention provides a method for ring-opening copolymerization of macrocyclic (ketal-ester) and macrocyclic lactone monomers, comprising: using a transesterification catalyst at high temperature and in the presence of an initiator, initiating an entropy-driven ring-opening polymerization reaction of the macrocyclic (ketal-ester) represented by Formula III and the macrocyclic lactone represented by Formula VI, as shown below:

[0029]

[0030] Among them, R 5 Represents one or more substituents on a macrolide monomer, selected from H, alkyl, substituted alkyl, halogen, alkoxy, cyano, aryl, etc.; x is an integer from 9 to 50. The long chain shown may contain one or more carbon-carbon double bonds and / or carbon-carbon triple bonds, and may also contain heteroatoms such as oxygen atoms, nitrogen atoms, and / or sulfur atoms. That is, the macrocyclic lactones shown in Formula VI include macrocyclic lactone derivatives containing unsaturated carbon atoms such as double bonds and / or triple bonds, as well as heteroatoms such as oxygen atoms, nitrogen atoms, and / or sulfur atoms. m and n represent the degree of polymerization, which is determined by the molecular weight of the polymer. The preferred polymer should have a molecular weight greater than 20 kDa.

[0031] The halogens mentioned above include fluorine, chlorine, bromine, and iodine; the alkyl groups mentioned above are preferably C1-C20 alkyl groups, more preferably C1-C6 alkyl groups; the substituents on the substituted alkyl groups include alkenyl, alkynyl, halogen, amide, alkoxy, cyano, aryl, etc.; the amide groups mentioned above are preferably C2-C20 amide groups, more preferably C1-C6 amide groups; the alkoxy groups mentioned above are preferably C2-C20 alkoxy groups, more preferably C1-C6 alkoxy groups; the aryl groups mentioned above are preferably C6-C12 aryl groups, such as phenyl.

[0032] The macrocyclic (ketal-ester) monomers represented by Formula III include, but are not limited to, HOD. The macrocyclic lactone monomers represented by Formula VI include, but are not limited to, decadecyl lactone (hereinafter referred to as PDL). Taking the ring-opening copolymerization of HOD and decadecyl lactone (PDL) as an example, the reaction equation is as follows:

[0033]

[0034] Furthermore, the preferred feed ratio of the macrocyclic lactone shown in Formula VI is 1% to 50% molar ratio of the two comonomers (not limited thereto). Since the ring-opening polymerization of both the macrocyclic (ketal-ester) shown in Formula III and the macrocyclic lactone shown in Formula VI is driven by entropy increase, the reaction temperature should be high, generally 80℃ to 260℃, preferably 120℃ to 200℃. To ensure uniform dispersion of the macrocyclic lactone fragments in the polymer backbone, the copolymerization reaction time should be longer than 3 hours.

[0035] Further, the initiator includes, but is not limited to, alcohol initiators such as ethanol, isopropanol, and benzyl alcohol. Further, the transesterification catalyst includes, but is not limited to, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), stannous octoate, stannous isooctanoate, titanate, etc., which are commercially available reagents and require no special treatment. Preferably, a titanate catalyst is used, with the general chemical formula Ti(OR')4, where R' is an alkyl group, such as tetraisopropyl titanate (Ti(Oi-Pr)4) and tetrabutyl titanate (Ti(On-Bu)4). When using a titanate catalyst for ring-opening polymerization, the titanate catalyst can also act as an initiator, eliminating the need for additional initiator addition. The catalyst is used in an amount based on a molar ratio of 0.01% to 10% of the two monomers.

[0036] Furthermore, the copolymerization reaction is carried out under anhydrous and oxygen-free conditions, either in bulk or in solution. The polymerization solvent is a solvent with a boiling point above 100°C, selected from toluene, xylene, chlorobenzene, dichlorobenzene, trichlorobenzene, diphenyl ether, etc., with chlorobenzene being preferred. All solvents are refluxed with metallic sodium to remove water before use, stored under a nitrogen atmosphere, and then... Molecular sieve.

[0037] Furthermore, the post-polymerization purification process includes precipitation and drying. The unsuitable solvents used in the precipitation process are selected from anhydrous methanol, diethyl ether, and saturated alkane solvents (such as n-pentane, n-hexane, cyclohexane, etc.), with anhydrous methanol being preferred as the precipitation solvent. Precipitation and centrifugation are carried out at room temperature. The polymer is then placed in a vacuum oven at 20–50°C overnight to remove residual solvent and complete the drying process.

[0038] Fourthly, the present invention provides a method for the highly selective chemical recovery in solution of a poly(ketal-ester) homopolymer (i.e., formula V) or copolymer (i.e., formula VII) to a macrocyclic (ketal-ester) (i.e., formula III), comprising: dissolving the poly(ketal-ester) homopolymer of formula V or the poly(ketal-ester) copolymer of formula VII in an aprotic solvent such as toluene, tetrahydrofuran, etc., and using an organic base catalyst at room temperature or under heating conditions to catalyze the highly selective depolymerization of the polymer back to the monomer, as shown below:

[0039]

[0040] Furthermore, the organic base catalyst includes, but is not limited to, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), phosphazene base-P1, phosphazene base-P2, phosphazene base-P4, and potassium tert-butoxide, which are commercially available reagents requiring no special treatment. Potassium tert-butoxide is preferred. The catalytic dosage of the organic base catalyst is 0.1% to 10% by mass of the poly(ketal-ester) polymer.

[0041] Furthermore, the depolymerization is carried out under solution conditions. The solvent is an aprotic solvent capable of dissolving the polymer, selected from toluene, xylene, chlorobenzene, tetrahydrofuran, dichloromethane, chloroform, etc., which are commercially available reagents that do not require special treatment; toluene is preferred. In some embodiments of the present invention, the polymer concentration is 200 mg / mL (not limited thereto).

[0042] Furthermore, the depolymerization reaction temperature is 0℃~120℃, and the reaction time is 1 minute to 240 hours.

[0043] Further, the post-depolymerization treatment includes washing, filtration, and drying. The solvent used in the washing process is selected from dichloromethane, chloroform, ethyl acetate, acetone, tetrahydrofuran, anhydrous methanol, diethyl ether, and saturated alkane solvents (such as n-pentane, n-hexane, cyclohexane, etc.). Acetone and dichloromethane are preferred as washing solvents. In some embodiments of the present invention, the washing-filtration operation is repeated three times at room temperature at a ratio of 15 mL of washing solvent per 10 g of crude product (not limited thereto). The white powder or colorless crystals obtained after washing and filtration are placed in a vacuum oven at 20°C to 50°C overnight to remove residual solvent and complete the drying process, thereby recovering high-purity monomers that can be repolymerized.

[0044] Fourthly, the present invention provides a method for the alcoholysis of copolymers of macrocyclic (ketal-ester) and macrocyclic lactones (i.e., formula VII), the specific reaction formula of which is as follows:

[0045]

[0046] Among them, R 6 The alkyl group represents an alkyl group, preferably an alkyl group having 1 to 20 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, etc. Methanol is more preferably used, in an amount of 10 to 50 equivalents of the polymer ester group content.

[0047] Furthermore, the catalyst for the alcoholysis reaction can be an organic base such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) being preferred, and the amount used is in the range of 1% to 20% molar ratio of the polymer ester group content.

[0048] Furthermore, the alcoholysis reaction was carried out in a sealed Shrek tube at a temperature of 60–140°C for a time of 0.5–12 hours.

[0049] Further, after the alcoholysis reaction is completed, the system is cooled to room temperature, and the unreacted alcohol is removed by vacuum distillation to obtain a mixture of compound VIII and compound IX; the mixture is then placed in a vacuum oven at 20°C to 50°C overnight to complete the drying process.

[0050] Fifthly, the present invention provides a method for the recondensation polymerization of small molecules after alcoholysis, the specific reaction formula of which is as follows:

[0051]

[0052] Furthermore, the catalyst for the re-condensation polymerization is selected from titanate compounds, preferably tetraisopropyl titanate (Ti(Oi-Pr)4) and tetrabutyl titanate (Ti(On-Bu)4), etc., and its amount should be less than 5% molar ratio of the content of hydroxyl or ester groups at the end of the polymer chain.

[0053] Furthermore, the polymerization reaction is carried out under bulk conditions, with a reaction temperature of 60℃ to 220℃ and a vacuum degree in the range of 5Pa to 200Pa.

[0054] Further, after the above reaction is completed, the polymer is dissolved. Solvents such as dichloromethane, trichloromethane, tetrachloromethane, tetrahydrofuran, toluene, and chlorobenzene can be used. Water, methanol, diethyl ether, ethanol, isopropanol, n-pentane, and n-hexane can be used as unsuitable solvents. The polymer is then precipitated, centrifuged, filtered, washed, and purified. The polymer is then placed in a vacuum oven at 20℃ to 50℃ overnight to remove residual solvents and complete the drying process.

[0055] The beneficial effects of the technical solution of the present invention mainly include:

[0056] 1. The macrocyclic (ketal-ester) synthesis method proposed in this invention is simple and highly efficient in purification. By selecting and mixing solvents, the macrocyclic (ketal-ester) is continuously precipitated from the system, avoiding the use of high dilution conditions. Therefore, compared with traditional macrocyclic synthesis, this invention does not require the use of large amounts of solvent and has a short reaction time. The obtained macrocyclic (ketal-ester) powder has strong crystallinity and low impurity content, requiring only simple washing and drying to obtain high-purity monomers, without the need for cumbersome chromatographic column purification and recrystallization purification.

[0057] 2. The macrocyclic (ketal-ester) ring-opening polymerization proposed in this invention is carried out at high temperatures in industrial production, which avoids the requirement that polymers that can be chemically recycled to monomers need to be polymerized at lower temperatures (e.g., below zero degrees Celsius), thus reducing production energy consumption.

[0058] 3. The poly(ketal-ester) proposed in this invention is thermodynamically more stable than macrocyclic (ketal-ester) monomers at high temperatures and will not spontaneously cyclize back to macrocyclic monomers during thermal processing, thus eliminating the need for rigorous purification and catalyst removal. Because polymerization occurs at high temperatures, the polymer has low viscosity, allowing for direct polymer processing, reducing purification steps and lowering production costs.

[0059] 4. The poly(ketal ester) proposed in this invention has widely tunable substituents, which can change the crystallinity, mechanical properties and other properties of the material according to different substituents. It can synthesize a series of chemically recyclable polymer materials with widely tunable properties and suitable for a variety of application scenarios.

[0060] 5. The poly(ketal-ester) proposed in this invention can be rapidly cyclized back to a macrocyclic (ketal-ester) under mild conditions in solution via organic base catalyst. The macrocyclic (ketal-ester) crystals precipitate out, requiring only filtration, washing, and drying to recover the high-purity monomer. Compared to monomer recovery and purification via high-temperature and high-vacuum distillation, the recovery method proposed in this invention is simpler to operate, requires less energy, and has higher separation efficiency. The crystallization precipitation promotes equilibrium, avoiding the use of high-dilution depolymerization conditions, requiring less solvent and shorter processing time.

[0061] 6. The macrocyclic (ketal-ester) and macrocyclic lactone copolymers proposed in this invention can synthesize a series of chemically recyclable polymer materials with widely tunable properties suitable for various application scenarios by changing the type of comonomer and the copolymerization ratio. These materials achieve properties comparable to commercially available non-degradable materials. For example, the copolymer synthesized by feeding HOD and pentadecyl lactone in a 3:1 ratio has better mechanical properties than commercial low-density polyethylene materials and has the potential to be applied to chemically recyclable packaging materials.

[0062] 7. The macrocyclic (ketal-ester) and macrocyclic lactone copolymer proposed in this invention can be rapidly cyclized back to the macrocyclic (ketal-ester) under mild conditions in solution via organic base catalyst, achieving selective chemical recovery of a single component of the copolymer. Alternatively, it can be broken down through alcoholysis, achieving chemical recovery of all components of the copolymer. The alcoholysis product can be further polycondensed at high temperature to obtain polymers of similar molecular weight while retaining the polymer's material properties, which is of significant importance.

[0063] In summary, this invention provides an efficient synthetic method for macrocyclic (ketal-ester) polymers and synthesizes a series of novel poly(ketal-ester) materials through ring-opening polymerization and ring-opening copolymerization. These poly(ketal-ester) polymers can be polymerized at industrial production temperatures, can be thermoformed without strict catalyst removal, have adjustable material properties, and can achieve monomer recovery under mild conditions, making them promising for large-scale applications and a new generation of green polymer materials. Attached Figure Description

[0064] Figure 1 The structure of the macrocyclic (ketal-ester) synthesized in this invention is shown, as well as the synthesis of a series of poly(ketal-ester) materials by ring-opening polymerization and ring-opening copolymerization.

[0065] Figure 2 The molecular structures of some compounds with 4-ketocarboxylic acid structures, compounds with 1,1,1-trihydroxymethyl structures, and some examples of macrocyclic lactones are shown.

[0066] Figure 3 Thermogravimetric curve of PHOD, 5% weight loss temperature (T d,5％ The temperature was 353℃ (heating rate was 20℃ / min).

[0067] Figure 4 The thermogravimetric curve of PHOD containing 0.5% Ti(Oi-Pr)4 is given by T. d,5％ The temperature is 345℃ (heating rate is 20℃ / min).

[0068] Figure 5 Comparison of HOD before polymerization, PHOD after polymerization, and HOD after chemical recovery (1H NMR spectrum). 1 HNMR, 400MHz, CDCl3).

[0069] Figure 6 The gel permeation chromatography elution time of PHOD-co-PPDL before methanol hydrolysis and PHOD-co-PPDL after methanol hydrolysis was used as a control (test temperature 30℃, mobile phase tetrahydrofuran, reference sample polystyrene standard sample). Detailed Implementation

[0070] To make the various technical features, advantages, or effects of the present invention more apparent and understandable, the following embodiments are provided for detailed description.

[0071] Example 1: Synthesis of macrocyclic (ketal-ester) HOD

[0072]

[0073] 17.4 g (150 mmol, 1.0 equiv) of levulinic acid and 18.0 g (150 mmol, 1.0 equiv) of 1,1,1-tris(hydroxymethyl)ethane were added to a 1 L round-bottom flask. 0.3 g of p-toluenesulfonic acid and 600 mL of a mixed solution of toluene and cyclohexane (v / v = 1 / 1) were added. A Dean-Stark receiving apparatus was installed, and the mixture was refluxed and stirred in an oil bath at 125 °C. After 12 h, sufficient water (approximately 5.4 mL) was collected, and reflux was stopped. The white solid precipitated in the flask was collected by filtration and washed once with dichloromethane and twice with acetone. The solid was dried in a vacuum oven at 50 °C for 6 h to obtain a white powdery solid HOD with a yield of 81%.

[0074] Its NMR data are as follows: 1 H NMR (400MHz, CDCl3) δ (TMS, ppm): 4.44 (s, 2H), 3.66 (s, 4H), 2.49–2.34 (m, 2H), 2.16–1.97 (m, 2H), 1.45 (s, 3H), 0.68 (s, 3H). 13 C NMR (100MHz, CDCl3) δ (TMS, ppm): 174.38, 98.44, 65.92, 64.77, 37.24, 33.32, 28.26, 18.08, 17.52.

[0075] Example 2: Synthesis of macrocyclic (ketal-ester) EtHOD

[0076]

[0077] 17.4 g (150 mmol, 1.0 equiv) of levulinic acid and 20.1 g (150 mmol, 1.0 equiv) of 1,1,1-trimethylolpropane were added to a 1 L round-bottom flask. 0.3 g of p-toluenesulfonic acid and 600 mL of a mixed solution of toluene and cyclohexane (v / v = 1 / 1) were added. A Dean-Stark receiving apparatus was installed, and the mixture was refluxed and stirred in an oil bath at 125 °C. After 12 h, sufficient water (approximately 5.4 mL) was collected, and reflux was stopped. The white solid precipitated in the flask was collected by filtration and washed once with dichloromethane and twice with acetone. The solid was dried in a vacuum oven at 50 °C for 6 h to obtain a white powdery solid HOD with a yield of 63%.

[0078] Its NMR data are as follows: 1 H NMR (400MHz, CDCl3) δ (TMS, ppm): 4.50 (s, 2H), 3.69 (s, 4H), 2.44–2.37 (m, 2H) ,2.10–2.02(m,2H),1.44(s,3H),1.11(q,J=7.6Hz,2H),0.79(t,J=7.6Hz,3H).

[0079] 13 C NMR (100MHz, CDCl3) δ (TMS, ppm): δ 173.28, 97.58, 63.99, 60.87, 36.13, 34.51, 27.29, 23.17, 17.18, 5.70.

[0080] Example 3: Ring-opening polymerization of macrocyclic (ketal-ester) HOD

[0081]

[0082] Synthesis of polymers containing catalysts: A typical polymerization experiment with a monomer to initiator ratio of 200:1 was taken as an example. In a nitrogen-protected glove box, 600 mg (1.5 mmol, 200 equiv) of HOD synthesized in Example 1 and 2.84 mg (0.01 mmol, 1 equiv) of Ti(Oi-Pr)4 were added to a reaction tube. After adding 0.5 mL of chlorobenzene, the tube cap was tightened and the tube was removed from the glove box. The tube was then placed in a 170°C oil bath and stirred for 6 h. The system gradually became clear and gelled. After cooling to room temperature, 0.05 mL of the reaction solution was taken using a dropper for further processing. 1 The monomer conversion was characterized by 1H NMR. The remaining polymer was reheated to 210 °C and the vacuum was reduced to 20 Pa for 30 minutes to remove the reaction solvent and the remaining monomer, yielding PHOD containing 0.5% Ti(Oi-Pr)4 with a yield of 85%, a molecular weight of 29.1 kDa, and a dispersion of 2.1.

[0083] Catalyst-free polymer synthesis: A typical polymerization experiment with a monomer to initiator ratio of 200:1 was used as an example. In a nitrogen-protected glove box, 600 mg (1.5 mmol, 200 equiv) of HOD synthesized in Example 1 and 2.84 mg (0.01 mmol, 1 equiv) of Ti(Oi-Pr)4 were added to a reaction tube. After adding 0.5 mL of chlorobenzene, the tube cap was tightened and the tube was removed from the glove box. The tube was then placed in a 170°C oil bath and stirred for 6 hours. The system gradually became clear and gelled. After cooling to room temperature, 0.05 mL of the reaction solution was taken using a dropper for further processing. 1The monomer conversion rate was characterized by 1H NMR. The remaining polymer was dissolved in dichloromethane, precipitated in methanol and centrifuged. The dissolution and precipitation process was repeated three times. The polymer was dried in a vacuum oven at 50°C for 8 hours to obtain a white blocky polymer PHOD with a yield of 84%, a molecular weight of 33.2 kDa, and a dispersion of 1.6.

[0084] The PHOD NMR data are as follows: 1 H NMR (400MHz, CDCl3) δ (TMS, ppm): 4.17 (s, 2H), 3.69–3.55 (m, 4H), 2.52 (dd, J = 9.1, 6.8Hz, 2H), 1.98 (dd, J = 9.0, 6.9Hz, 2H), 1.41 (s, 3H), 0.78 (s, 3H).

[0085] 13 C NMR (100MHz, CDCl3) δ (TMS, ppm): 173.68, 98.23, 66.39, 66.02, 36.13, 33.33, 28.07, 17.92, 17.58.

[0086] 10 mg of the polymer containing the catalyst from Example 3 was weighed and subjected to thermogravimetric analysis (TGA). The temperature was increased from room temperature to 800°C at a rate of 20°C / min. The test atmosphere was nitrogen. The test results are as follows: Figure 3 As shown. 10 mg of the polymer without the catalyst from Example 3 was weighed and subjected to a thermogravimetric test. The temperature was increased from room temperature to 800°C at a rate of 20°C / min. The test atmosphere was nitrogen. The test results are shown below. Figure 4 As shown.

[0087] Depend on Figures 3-4 It is evident that poly(ketal-ester) PHOD exhibits good thermal stability, even with a 5% weight loss temperature (T5) in the presence of an transesterification catalyst. d,5％ The temperature remains as high as 345℃, with a wide processing window.

[0088] Example 4: Synthesis of macrocyclic (ketal-ester) EtHOD

[0089]

[0090] Taking a typical polymerization experiment with a monomer to initiator ratio of 200:1 as an example, in a nitrogen-protected glove box, 624 mg (1.5 mmol, 200 equiv) of EtHOD synthesized in Example 2 and 2.84 mg (0.01 mmol, 1 equiv) of Ti(Oi-Pr)4 were added to a reaction tube. After adding 0.5 mL of chlorobenzene, the tube cap was tightened and the tube was removed from the glove box. The tube was then placed in a 170°C oil bath and stirred for 6 hours. The system gradually became clear and gelled. After cooling to room temperature, 0.05 mL of the reaction solution was taken using a dropper for further processing. 1 The monomer conversion rate was characterized by 1H NMR. The remaining polymer was dissolved in dichloromethane, precipitated in methanol and centrifuged. The dissolution and precipitation process was repeated three times. The polymer was dried in a vacuum oven at 50°C for 8 hours to obtain a white blocky polymer PHOD with a yield of 84%, a molecular weight of 32.4 kDa, and a dispersion of 1.7.

[0091] The PEtHOD NMR data are as follows: 1 H NMR (400MHz, CDCl3) δ (TMS, ppm): 4.22 (s, 2H), 3.71–3.59 (m, 4H), 2.55–2.46 (m, 2H), 1 .98(dd,J=9.0,6.9Hz,2H),1.40(s,3H),1.25(q,J=7.6Hz,2H),0.79(t,J=7.6Hz,3H).

[0092] 13 C NMR (100MHz, CDCl3) δ (TMS, ppm): δ173.63,98.44,65.02,63.42,35.99,35.53,28.15,24.01,18.08,6.80

[0093] Example 5: Ring-opening copolymerization of macrocyclic (ketal-ester) HOD and pentadecyl lactone PDL

[0094]

[0095] Taking a typical copolymerization experiment with monomers HOD:PDL = 3:1 as an example, in a nitrogen-protected glove box, 450 mg (0.125 mmol, 300 equiv) of HOD synthesized in Example 1, 90 mg (0.375 mmol, 100 equiv) of PDL, and 1.60 mg (0.0057 mmol, 1 equiv) of Ti(Oi-Pr)4 were added to a reaction tube. After adding 0.5 mL of chlorobenzene, the reaction tube was sealed and removed from the glove box. It was then placed in a 170°C oil bath and stirred for 5 h. After cooling to room temperature, 0.05 mL of the reaction solution was taken using a dropper for further processing. 1The monomer conversion was characterized by 1H NMR. The remaining polymer was dissolved in dichloromethane, and the precipitate was centrifuged in methanol. The dissolution and precipitation process was repeated three times. The polymer was then dried in a vacuum oven at 50°C for 8 hours to obtain a white, blocky polymer PHOD. 70 -co-PPDL 30 The yield was 85%, the molecular weight was 39.9 kDa, and the dispersibility was 1.9.

[0096] Similarly, with a total HOD and PDL concentration of 3 mol / L, and a molar ratio of HOD:PDL:Ti(Oi-Pr)4 = 100:300:1, PHOD was synthesized after 8 hours of reaction. 16 -co-PPDL 84 With a molar ratio of HOD:PDL:Ti(Oi-Pr)4 = 200:200:1, and a reaction time of 8 hours, PHOD was synthesized. 25 -co-PPDL 75 With a molar ratio of HOD:PDL:Ti(Oi-Pr)4 = 300:100:1, PHOD was synthesized after reacting for 8 hours. 44 -co-PPDL 56 With a molar ratio of HOD:PDL:Ti(Oi-Pr)4 = 300:60:1.5, PHOD was synthesized after reacting for 5 hours. 81 -co-PPDL 19 With a molar ratio of HOD:PDL:Ti(Oi-Pr)4 = 300:45:1.5, PHOD was synthesized after reacting for 5 hours. 86 -co-PPDL 14 With a molar ratio of HOD:PDL:Ti(Oi-Pr)4 = 300:30:1.5, PHOD was synthesized after reacting for 5 hours. 88 -co-PPDL 12 .

[0097] Example 6: Chemical recovery of PHOD to HOD

[0098]

[0099] In a nitrogen-filled glove box, 550 mg of the catalyst-free PHOD synthesized in Example 3 was added to a 4 mL sample vial and dissolved in 2.75 mL of toluene. After the polymer was completely dissolved, 49 μL of a 1 M potassium tert-butoxide THF solution was injected. The sample vial was shaken, and a large amount of precipitate was produced. The reaction was quenched with benzoic acid. The white solid was filtered, washed with toluene and acetone, and dried to constant weight in a vacuum oven at 50 °C. 535 mg of HOD powder was recovered, with a yield of 97%.

[0100] Example 7: Chemical recovery of PEtHOD to EtHOD

[0101]

[0102] In a nitrogen-filled glove box, 590 mg of PEtHOD synthesized in Example 4 was added to a 4 mL sample vial and dissolved in 2.75 mL of toluene. After the polymer was completely dissolved, 49 μL of a 1 M potassium tert-butoxide THF solution was injected. The sample vial was shaken, and a large amount of precipitate was produced. The reaction was quenched with benzoic acid. The white solid was filtered, washed with toluene and acetone, and dried to constant weight in a vacuum oven at 50 °C. 553 mg of HOD powder was recovered, with a yield of 94%.

[0103] Example 8: PHOD-co-PPDL (using PHOD) 70 -co-PPDL 30 Selective recycling of HOD (for example)

[0104]

[0105] In a nitrogen-filled glove box, 313 mg of the PHOD synthesized in Example 5 was added to a 4 mL sample vial. 81 -co-PPDL 19 The polymer was dissolved in 1.6 mL of toluene. After complete dissolution, 6.26 mg of TBD was added. The sample vial was sealed and removed from the glove box, heated at 80 °C for 48 hours, and the reaction was quenched with benzoic acid. The white solid was filtered, washed with toluene and acetone, and dried to constant weight in a vacuum oven at 50 °C. 201 mg of HOD powder was recovered, with a yield of 82%.

[0106] Example 9: PHOD-co-PPDL (using PHOD) 70 -co-PPDL 30 Methanol hydrolysis and recondensation polymerization (for example)

[0107]

[0108] Add 60 mg of the PHOD synthesized in Example 5 to a 10 mL Shrek tube in a glove box. 70 -co-PPDL 30 1.2 mg TBD and 0.3 mL methanol were added. The mixture was sealed in a Schlenk tube, removed from the glove box, and heated in an oil bath at 80 °C for one hour. After heating was stopped, excess methanol was removed by vacuum distillation to obtain an oily PHOD. 70 -co-PPDL 30 Methanol hydrolysis products.

[0109] To contain oily PHOD70 -co-PPDL 30 0.6 mg of Ti(On-Bu)4 was added to a Schlenk tube containing the methanol hydrolysis product. The tube was then evacuated and heated to 80 °C for 12 hours. The temperature was then increased to 120 °C and maintained for another 12 hours. The vacuum was then further reduced to below 20 Pa, and the temperature was increased to 150 °C and maintained for 1 hour.

[0110] The HOD synthesized in Example 1 was prepared into a 5 mg / mL deuterated chloroform solution and analyzed by 1H NMR spectroscopy; the catalyst-free PHOD synthesized in Example 3 was prepared into a 5 mg / mL deuterated chloroform solution and analyzed by 1H NMR spectroscopy; the HOD chemically recovered in Example 6 was prepared into a 5 mg / mL deuterated chloroform solution and analyzed by 1H NMR spectroscopy; the results of the three tests were compared as follows: Figure 5 As shown.

[0111] Take the PHOD synthesized in Example 5 70 -co-PPDL 30 A 10 mg / mL tetrahydrofuran solution was prepared and analyzed by tetrahydrofuran mobile phase gel permeation chromatography; the PHOD synthesized in Example 9 was taken. 70 -co-PPDL 30 A 10 mg / mL tetrahydrofuran solution was prepared for gel permeation chromatography analysis of tetrahydrofuran using a mobile phase; the results of the two tests were compared, for example... Figure 6 As shown.

[0112] Depend on Figures 5-6 It is evident that poly(ketal-ester) PHOD exhibits excellent chemical recyclability. The high-purity monomer HOD recovered can be re-ring-opened and polymerized to obtain the exact same PHOD. The poly(ketal-ester) copolymer PHOD-co-PPDL can be recovered by methanol hydrolysis to obtain small hydroxy ester molecules, and re-condensation polymerization can yield PHOD-co-PPDL with a similar degree of polymerization, achieving closed-loop recovery of all components.

[0113] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention should be covered within the protection scope of the present invention, which is defined by the claims.

Claims

1. A method for synthesizing a macrocyclic (ketal-ester) compound, comprising adding an acid catalyst to a mixed organic solution of a 4-ketocarboxylic acid compound of Formula I and a 1,1,1-trihydroxymethyl compound of Formula II, heating to carry out esterification and ketalization reactions, and dehydration cyclization to synthesize the macrocyclic (ketal-ester) compound of Formula III, as shown in the following reaction formula: in, R 1 selected from H, C1-C6alkyl; R 2 selected from H, C1-C6alkyl; R 3 selected from H, C1-C6alkyl; R 4 selected from H, C1-C6alkyl.

2. The method for synthesizing macrocyclic (ketal-ester) compounds as described in claim 1, characterized in that, The acid catalyst is selected from one or more of p-toluenesulfonic acid, sulfuric acid, and phosphoric acid; the solvent for the dehydration cyclization reaction is selected from one or more of toluene, xylene, n-hexane, and cyclohexane; the reaction temperature is 100℃~140℃, and the water generated during the reaction is collected and removed.

3. A macrocyclic (ketal-ester) structure as shown in Formula III: in, R 1 selected from H, C1-C6alkyl; R 2 selected from H, C1-C6alkyl; R 3 selected from H, C1-C6alkyl; R 4 selected from H, C1-C6alkyl.

4. A method for synthesizing poly(ketal-ester), using the macrocyclic (ketal-ester) shown in Formula III as a monomer, and initiating an entropy-driven ring-opening polymerization reaction under high temperature conditions using an ester exchange catalyst and an initiator to obtain the poly(ketal-ester) shown in Formula V, as shown below: in, n represents the degree of polymerization; R 1 selected from H, C1-C6 alkyl; R 2 selected from H, C1-C6 alkyl; R 3 selected from H, C1-C6 alkyl; R 4 selected from H, C1-C6 alkyl.

5. A method for ring-opening copolymerization of macrocyclic (ketal-ester) and macrocyclic lactone monomers, wherein the macrocyclic (ketal-ester) represented by Formula III and the macrocyclic lactone represented by Formula VI are subjected to an entropy-driven ring-opening polymerization reaction initiated by an initiator under high temperature conditions using an ester exchange catalyst, as shown below: in, R 1 Selected from H, C1~C6 alkyl; R 2 Selected from H, C1~C6 alkyl; R 3 Selected from H, C1~C6 alkyl; R 4 Selected from H, C1~C6 alkyl; R 5 Represents one or more substituents on a macrolide monomer, selected from H and C1-C6 alkyl groups; x is an integer from 9 to 50. The long chain shown may contain carbon-carbon double bonds, carbon-carbon triple bonds, and / or heteroatoms selected from oxygen, nitrogen, and sulfur atoms; m and n represent the degree of polymerization.

6. The method as described in claim 4 or 5, characterized in that, The transesterification catalyst is selected from 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, stannous octoate, stannous isooctanoate, and titanate.

7. The method as described in claim 4 or 5, characterized in that, The polymerization reaction occurs under anhydrous and oxygen-free conditions, with a reaction temperature of 80℃~260℃.

8. A chemically recyclable polymer material, which is a poly(ketal-ester) of Formula V, or a copolymer containing poly(ketal-ester) of Formula VII: in, R 1 Selected from H, C1~C6 alkyl; R 2 Selected from H, C1~C6 alkyl; R 3 Selected from H, C1~C6 alkyl; R 4 Selected from H, C1~C6 alkyl; R 5 Represents one or more substituents, selected from H and C1-C6 alkyl groups; x is an integer from 9 to 50. The long chain shown may contain carbon-carbon double bonds, carbon-carbon triple bonds, and / or heteroatoms selected from oxygen, nitrogen, and sulfur atoms; m and n represent the degree of polymerization.

9. A method for selectively and chemically recovering macrocyclic (ketal-ester) monomers from poly(ketal-ester) homopolymers or copolymers, comprising dissolving the poly(ketal-ester) homopolymer of formula V or the poly(ketal-ester) copolymer of formula VII in an aprotic solvent, and catalyzing the depolymerization of the polymer using an organic base catalyst at room temperature or under heating conditions to obtain the macrocyclic (ketal-ester) monomer of formula III, as shown below: in, R 1 Selected from H, C1~C6 alkyl; R 2 Selected from H, C1~C6 alkyl; R 3 Selected from H, C1~C6 alkyl; R 4 Selected from H, C1~C6 alkyl; R 5 Represents one or more substituents, selected from H and C1-C6 alkyl groups; x is an integer from 9 to 50. The long chain shown may contain carbon-carbon double bonds, carbon-carbon triple bonds, and / or heteroatoms selected from oxygen, nitrogen, and sulfur atoms; m, n, and y represent the degree of polymerization, where y is less than m.

10. The method as described in claim 9, characterized in that, The organic base catalyst is selected from 1,5,7-triazine-bicyclo[4.4.0]dec-5-ene, 1,8-diazabenzine-bicyclo[5.4.0]undec-7-ene, phosphazene base-P1, phosphazene base-P2, phosphazene base-P4, and potassium tert-butoxide.

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