[2.1. 1] bridged ring lactone monomer, recoverable polyester and preparation method of [2.1. 1] bridged ring lactone monomer and recoverable polyester

Abstract

The invention discloses a [2.1. 1] bridged ring lactone monomer, recyclable polyester and a preparation method of the [2.1. 1] bridged ring lactone monomer. A [2.1. 1] bridged ring lactone monomer as shown in a formula (I) and a metal catalyst are subjected to a ring-opening polymerization reaction in an organic solvent to generate the recyclable polyester with a main chain containing a four-membered ring as shown in a formula (II). The monomer shown in the formula (I) and other lactone monomers are subjected to ring-opening copolymerization, and a recoverable random copolymer or block copolymer can be prepared. The polyester compound prepared by the invention has the characteristics of high molecular weight and narrow dispersity, has excellent thermal properties, mechanical properties, hydrolysis-resistant stability and chemical degradability, and is a polyester material with high polymerization activity, high recoverability and high performance; and the product is expected to become a substitute of non-degradable commercial plastic low-density polyethylene and polystyrene at present. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of polymerization monomer synthesis and polymer synthesis, and in particular to a [2.1.1] bridged ring lactone monomer and a synthesis method thereof, a method for preparing a main chain four-membered ring-containing polyester by ring-opening (co)polymerization, and a method for efficiently degrading a polymer into a monomer. Background Art

[0002] Polymer materials are the most widely used artificial materials in the world. They are widely used in the production and life of human society due to their low cost, light weight, corrosion resistance, high strength, transparency, and low toxicity. Plastic is the most typical representative of polymer materials. According to statistics, in 2020, the output of plastics was about 367 million tons, and it is expected that by 2050, its output will reach about 1.1 billion tons. However, traditional plastic products pursue excellent performance and durability. After use, they are very difficult to degrade and are directly incinerated, landfilled or flow into the ocean. This linear model of "production-use-discard" has caused serious environmental pollution, ecological damage and waste of resources, and has brought huge difficulties to the sustainable development of the green material economy. The development of recyclable polymers can effectively alleviate this dilemma. The "monomer-polymer-monomer" cycle model allows polymer materials to be selectively recycled to obtain monomers after use for repolymerization or reuse.

[0003] Polyester is a class of polymer materials with good biocompatibility and biodegradability, and is a potential substitute for traditional full-carbon chain polymer materials that are difficult to degrade. Using cheap bulk chemicals as raw materials to synthesize monomers with high polymerization activity, and using efficient catalysts to prepare recyclable polyesters with excellent material properties through ring-opening polymerization is currently a research hotspot in the field of sustainable polymer materials. However, most of the reported recyclable polyesters still have problems such as complex monomer synthesis, polymer properties that are difficult to compare with commercial plastics (such as polyolefins), and low recycling efficiency. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of complex synthesis of current recyclable polyester monomers, limited polymer properties, difficulty in matching commercial plastics (such as polyolefins) and low recycling efficiency, and to provide a [2.1.1] bridged ring lactone monomer and a polyester containing a four-membered ring in the main chain and a preparation method thereof. The monomer designed by the present invention is prepared by a simple synthetic route using low-cost bulk chemicals as raw materials, has high polymerization activity, and is obtained by ring-opening (co)polymerization to obtain a polyester material with high molecular weight, narrow dispersion, excellent thermodynamic properties and high recycling efficiency.

[0005] The present invention achieves the above technical objectives through the following technical solutions.

[0006] In the first aspect of the present invention, there is provided a [2.1.1] bridged lactone monomer, the general structural formula of which is shown in formula (I):

[0007]

[0008] In formula (I), R is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl; the substituent in R is selected from alkyl, alkoxy, halogen, etc. Among them, the aryl is preferably a C6-C12 aryl, such as phenyl, naphthyl, biphenyl, alkyl substituted phenyl, alkoxy substituted phenyl, halogen substituted phenyl, etc.; the alkyl is preferably a C1-C12 straight chain or branched alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, trifluoromethyl, etc.; the alkoxy is preferably a C1-C12 alkoxy, such as methoxy, ethoxy, propoxy, etc.; the halogen includes fluorine, chlorine, bromine, and iodine.

[0009] R includes but is not limited to the following structures:

[0010]

[0011] Wherein, n is an integer greater than or equal to 0; X represents a halogen selected from F, Cl, Br, and I.

[0012] In a second aspect of the present invention, a method for synthesizing the above-mentioned [2.1.1] bridged lactone monomer is provided, comprising the following steps:

[0013] 1. When R is an alkyl group, the general reaction formula is as follows:

[0014]

[0015] (1a) dissolving 3-carbonyl-cyclobutanecarboxylic acid methyl ester in an organic solvent, adding a reducing agent under ice bath, stirring and reacting for a period of time (e.g., 30 to 60 minutes), quenching, extracting, washing, drying, and spinning the solvent to obtain 3-hydroxy-cyclobutanecarboxylic acid methyl ester;

[0016] (1b) In an ice bath, slowly add an organic solution of methyl 3-hydroxy-cyclobutanecarboxylate to a non-nucleophilic strong base solution, stir, return to room temperature and stir for a period of time (e.g., 30 to 90 minutes), then add alkyl iodide dropwise, stir overnight; add an acid solution to quench, extract, wash, and spin dry the solvent to obtain intermediate a;

[0017] (1c) Mixing intermediate a with a strong base solution, stirring and reacting for a period of time (e.g., 2 to 3 hours), adding an acid solution to quench the reaction, extracting, washing, drying, and spinning the solvent to obtain intermediate b;

[0018] (1d) Dissolve the intermediate b in an organic solvent, add a condensing agent and HOBt (1-hydroxybenzotriazole), stir and react for a period of time (e.g., 20 to 60 minutes), extract, wash, and dry to obtain the target monomer alkyl-substituted [2.1.1] bridged ring lactone.

[0019] In the above step (1a), the organic solvent can be selected from one or more of methanol, ethanol, N,N-dimethylformamide, and tetrahydrofuran; the reducing agent can be selected from one or more of sodium borohydride, methylmagnesium bromide, phenylmagnesium bromide, and benzylmagnesium bromide.

[0020] In the above step (1b), the alkyl group in the alkyl iodide is preferably one of C1-C12 alkyl, C1-C12 alkoxy, and halogenated alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, trifluoromethyl, methoxy, ethoxy, propoxy, etc.; the organic solvent can be selected from one or more of tetrahydrofuran, ether, and n-hexane; the strong base in the non-nucleophilic strong base solution can be one of diisopropyl lithium amide and bistrimethylsilyl lithium amide; the acid solution can be one of 1-5M hydrochloric acid and sulfuric acid solution.

[0021] In the above step (1c), the strong alkaline solution may be one of sodium hydroxide, lithium hydroxide and potassium hydroxide solutions; the acid solution may be one of 1-5M hydrochloric acid and sulfuric acid solutions.

[0022] In the above step (1d), the organic solvent can be selected from one or more of dichloromethane, chloroform, tetrahydrofuran, ether, toluene, and ethyl acetate; the condensing agent can be one of EDCI (1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride), DCC (1,3-dicyclohexylcarbodiimide) and DIC (N,N-diisopropylcarbodiimide).

[0023] 2. When R is an aromatic group, the general reaction formula is as follows:

[0024]

[0025] (2a) dissolving triphosgene in an organic solvent, placing it in an ice bath, slowly adding a mixed organic solution of ethanol and a nucleophilic agent, reacting for a period of time (e.g., 30 to 60 minutes) under ice bath conditions, warming to room temperature and reacting for a period of time (e.g., 2 to 3 hours), then washing with water, drying, and removing the solvent to obtain ethyl chloroformate;

[0026] (2b) adding an organic solution of arylacetic acid and epichlorohydrin to a Grignard reagent under ice bath conditions, stirring, reacting at room temperature for a period of time (e.g., 40 to 60 minutes), then adding more Grignard reagent, heating at 50 to 60° C. for a relatively long time (e.g., 14 to 16 hours); after the reaction is completed, adding an acid solution to quench, extracting, washing, drying, spinning the solvent to dryness, and adding a poor solvent for crystallization to obtain an intermediate c;

[0027] (2c) Dissolve the intermediate c in an organic solvent, add an acid-binding agent thereto, place in an ice bath, then add ethyl chloroformate, react for a period of time (e.g., 30 to 60 minutes), return to room temperature, and react for a longer period of time (e.g., 20 to 24 hours); extract, wash, dry, and spin-dry the solvent to obtain the target monomer aromatic-substituted [2.1.1] bridged ring lactone.

[0028] In the above step (2a), the organic solvent can be selected from one or more of dichloromethane, chloroform, tetrahydrofuran, diethyl ether, and toluene; the nucleophilic reagent can be selected from one of triethylamine, pyridine, N,N-diisopropylethylamine and dimethylformamide.

[0029] In the above step (2b), the aryl group in the arylacetic acid can be one of phenyl, naphthyl, biphenyl, alkyl-substituted phenyl, alkoxy-substituted phenyl, and halogenated phenyl, wherein the alkyl group in the alkyl-substituted phenyl is preferably a C1-C12 alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, trifluoromethyl, etc., the alkoxy group in the alkoxy-substituted phenyl is preferably a C1-C12 alkoxy group, such as methoxy, ethoxy, propoxy, etc., and the halogen in the halogenated phenyl is preferably fluorine, chlorine, bromine, and iodine.

[0030] The organic solvent in step (2b) can be selected from one or more of dichloromethane, tetrahydrofuran, toluene and ethyl acetate.

[0031] The Grignard reagent in step (2b) can be selected from one of isopropylmagnesium chloride, methylmagnesium chloride and phenylmagnesium chloride; when the reaction needs to add the Grignard reagent, it must be carried out under the protection of an inert gas (such as nitrogen, argon, etc.). The acid solution is one of 1-5M hydrochloric acid and sulfuric acid solutions.

[0032] In the above step (2c), the acid binding agent can be one of triethylamine, n-butylamine, diethylmethylamine, and pyridine; the organic solvent can be one or more selected from dichloromethane, chloroform, tetrahydrofuran, ether, and toluene.

[0033] In the third aspect of the present invention, a polyester having a main chain containing a four-membered ring prepared from the above-mentioned [2.1.1] bridged ring lactone monomer is provided, and its general structural formula is shown in formula (II):

[0034]

[0035] Wherein, n is the degree of polymerization, and the value is 37-9600; R is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl. As mentioned above, R can be selected from the following structures:

[0036]

[0037] The number average molecular weight of the polyester represented by formula (II) provided by the present invention is greater than or equal to 6.6 kg / mol, preferably 6.6 to 531 kg / mol, and the molecular weight distribution is 1.0 to 2.0, preferably 1.02 to 1.86.

[0038] In a fourth aspect of the present invention, a method for synthesizing the polyester represented by the above formula (II) is provided, and the specific steps are as follows:

[0039] The [2.1.1] bridged ring lactone monomer compound represented by formula (I) is subjected to a ring-opening polymerization reaction in an organic solvent in the presence of a metal catalyst to obtain a polyester represented by formula (II).

[0040] In the above technical solution, the metal catalyst can be one of the following structural compounds:

[0041]

[0042] In some cases, an initiator needs to be added, and the initiator is mainly an alcohol compound, preferably one selected from benzyl alcohol, isopropanol, and 2,2-diphenylethanol.

[0043] The organic solvent may be a combination of one or more of dichloromethane, chloroform, toluene and tetrahydrofuran.

[0044] In the ring-opening polymerization reaction, the molar concentration of the compound represented by formula (I) in the organic solvent is preferably 1.0 to 2.6 mol / L; the molar ratio of the compound represented by formula (I) to the metal catalyst is 50:1 to 2500:1; and the molar ratio of the metal catalyst to the initiator is 1:1 to 1:3.

[0045] The above ring-opening polymerization reaction is carried out under an inert gas atmosphere; the reaction temperature is room temperature (20-30° C.); and the reaction time is 1 min to 35 h.

[0046] In a fifth aspect of the present invention, a method for preparing linear or cyclic polyesters with different topological structures is provided, wherein the specific steps are as follows:

[0047] The compound represented by formula (I) is subjected to a ring-opening polymerization reaction in an organic solvent in the presence of a catalyst to obtain polyesters represented by formula (II) with different topological structures;

[0048] The catalyst used to prepare the linear polymer is one of Y1, Zn1, La1+initiator, and Y2+initiator, and the catalyst used to prepare the cyclic polymer is one of La1, Y2, t One of the BuOKs;

[0049] The initiator is an alcohol compound, preferably one of benzyl alcohol, isopropanol and 2,2-diphenylethanol.

[0050] In a sixth aspect of the present invention, a method for recovering a monomer from a polymer under catalyst conditions is provided, and the specific operation is as follows:

[0051]

[0052] In the solution degradation recovery, the polymer represented by formula (II) and the catalyst are mixed into a solution and heated to achieve the conversion of the polymer into a monomer; wherein the catalyst used is Sn(Oct)2, ZnCl2, YCl3, LaCl3, TBD, DMAP, t Any one of BuOK, Y1, Y2, Zn1, La1 and Y(CH2SiMe3)3(THF)2, and the solvent used is one of toluene, xylene and 1,2-dichlorobenzene.

[0053] In the bulk molten state recovery, the polymer represented by formula (II) is mixed with a catalyst and heated to achieve the conversion of the polymer to the monomer; wherein the catalyst used is Sn(Oct)2, ZnCl2, YCl3, LaCl3, TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene), DMAP (4-dimethylaminopyridine), t Any one of BuOK, Y1, Y2, Zn1, La1 and Y(CH2SiMe3)3(THF)2.

[0054] The present invention also studies the thermal properties, mechanical properties and hydrolysis resistance of the polyester compound represented by formula (II).

[0055] The polyester compound represented by formula (II) prepared by the present invention has an initial decomposition temperature of 372-380°C, a glass transition temperature of 19-110°C, a melting point of 92-241°C, and has excellent thermal properties and crystallinity.

[0056] The polyester represented by formula (II) has a tensile strength of 25.3-30.6 MPa, an elongation at break of 4.9-500%, and a Young's modulus of 446-1560 MPa, and has excellent mechanical properties.

[0057] The polyester represented by formula (II) is prepared into a polymer film by a solvent volatilization method. After being placed in acidic, alkaline and neutral aqueous solutions for 60 days, there is no obvious quality change and the film has excellent anti-hydrolysis properties.

[0058] In the seventh aspect of the present invention, there is provided a recyclable polyester [2.1.1] prepared by ring-opening copolymerization of a bridged lactone monomer and other lactone monomers, which is one or more of a random copolymer and a block copolymer, and the general structural formula is shown in formula (III):

[0059]

[0060] Wherein, n and m are the degree of polymerization, and both are greater than or equal to 10; x is an integer greater than or equal to 1, and the main body of other lactone monomers is one or more of γ-butyrolactone, δ-valerolactone, ε-caprolactone, δ-caprolactone, and 7-heptanolactone; R 1 is one or more of hydrogen, C1-C12 alkyl, C1-C12 alkoxy, halogen, C6-C12 aryl; R is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl; as mentioned above, R can be selected from the following structures:

[0061]

[0062] In an eighth aspect of the present invention, a method for synthesizing the above copolymer is provided, wherein the specific steps are as follows:

[0063]

[0064] One-pot method: the compound represented by formula (I) is mixed with the second lactone monomer, and then a metal catalyst and an initiator are added to carry out a ring-opening copolymerization reaction in an organic solvent to obtain a random copolymer or block copolymer represented by formula (III).

[0065] Sequential addition: a lactone monomer is first mixed with a metal catalyst and an initiator in an organic solvent to generate a first-stage homopolymer, and then a second lactone monomer is added to the system to generate a second-stage polymer to obtain a block copolymer shown in formula (III).

[0066] In the above synthesis method, the metal catalyst may be one of the following structural compounds:

[0067]

[0068] The initiator is an alcohol compound, preferably one of benzyl alcohol, isopropanol, 2,2-diphenylethanol, 1,4-phenylenediol, 1,4-butanediol, and 1,6-hexanediol;

[0069] The organic solvent is a combination of one or more of dichloromethane, chloroform, toluene and tetrahydrofuran;

[0070] The polymerization reaction is carried out under an inert gas atmosphere; the reaction temperature is room temperature (20-30°C).

[0071] In summary, the present invention uses cheap bulk chemicals as raw materials to design and synthesize [2.1.1] bridged ring lactone monomers, which have large ring tension and can be efficiently ring-opened polymerized at room temperature to obtain polyesters containing four-membered rings in the main chain, with a number average molecular weight of 6.6 to 531 kg / mol, up to 531 kg / mol, and a molecular weight distribution of mostly less than 1.2. Compared with existing recyclable polyester materials, the advantages of the present invention are specifically embodied in:

[0072] 1) The monomer synthesis steps are simple, the raw materials are cheap and readily available, and monomers containing different substituents can be easily prepared, which is suitable for large-scale production;

[0073] 2) The monomer has high polymerization activity and can be rapidly ring-opened and polymerized at room temperature to obtain the target polymer with a number average molecular weight of up to 531

[0074] kg / mol, the molecular weight distribution is mostly less than 1.2, and the polymerization process is highly controllable;

[0075] 3) The polyester compound in the present invention has high thermal stability, and the initial decomposition temperature is as high as 380°C;

[0076] 4) The thermal properties of the polyester compounds of the present invention can be adjusted according to the side chain substituents, and all have excellent thermal properties and crystallinity properties, with a glass transition temperature of up to 110°C and a melting point of up to 241°C;

[0077] 5) The mechanical properties of the polyester compound of the present invention can be adjusted according to the side chain substituents, and the tensile strength can reach up to 30.6 MPa, the elongation at break can reach up to 500%, and the Young's modulus can reach up to 1.56 GPa;

[0078] 6) The polyester compound of the present invention has excellent hydrolysis resistance and has no obvious quality change after being immersed in acidic, alkaline and neutral aqueous solutions for 60 days;

[0079] 7) The polyester compound in the present invention has excellent degradation recovery properties, and after being mixed with a catalyst (and a solvent) and heated, the monomer can be efficiently recovered;

[0080] 8) The polyester compound in the present invention is comparable to commercial plastics such as low-density polyethylene and polystyrene in terms of thermal and mechanical properties, and can be efficiently degraded and recycled under specific conditions, and is a potential substitute for low-density polyethylene and polystyrene.

[0081] 9) The [2.1.1] bridged lactone in the present invention can be ring-opening copolymerized with other lactone monomers to facilitate the preparation of random copolymers and block copolymers, and to develop recyclable polyester materials with more diverse properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 The H NMR spectrum of the [2.1.1] bridged lactone Bu-BL monomer prepared in Example 1 ( 1 1H NMR).

[0083] Figure 2 The carbon NMR spectrum of the [2.1.1] bridged lactone Bu-BL monomer prepared in Example 1 ( 13 C NMR).

[0084] Figure 3 This is the H NMR spectrum of the [2.1.1] bridged lactone Ph-BL monomer prepared in Example 2 ( 1 1H NMR).

[0085] Figure 4 The carbon NMR spectrum of the bridged lactone Ph-BL monomer [2.1.1] prepared in Example 2 ( 13 C NMR).

[0086] Figure 5 The hydrogen nuclear magnetic resonance spectrum of the polyester P(Bu-BL) prepared in Example 3 ( 1 1H NMR).

[0087] Figure 6 The carbon NMR spectrum of the polyester P(Bu-BL) prepared in Example 3 ( 13 C NMR).

[0088] Figure 7 The H NMR spectrum of the polyester P(Ph-BL) prepared in Example 4 ( 1 1H NMR).

[0089] Figure 8 The carbon NMR spectrum of the polyester P (Ph-BL) prepared in Example 4 ( 13 C NMR).

[0090] Fig. 9 This is the GPC spectrum of the polyester P(Bu-BL) prepared in Example 3.

[0091] Fig.10 This is the GPC spectrum of the polyester P (Ph-BL) prepared in Example 4.

[0092] Fig.11This is the TGA spectrum of the polyester P(Bu-BL) prepared in Example 3.

[0093] Fig.12 This is the DSC spectrum of the polyester P(Bu-BL) prepared in Example 3.

[0094] Fig.13 This is the TGA spectrum of the polyester P (Ph-BL) prepared in Example 4.

[0095] Fig.14 This is the DSC spectrum of the polyester P (Ph-BL) prepared in Example 4.

[0096] Fig.15 XRD spectra of the polyester P(Bu-BL) prepared in Example 3 and the polyester P(Ph-BL) prepared in Example 4.

[0097] Fig.16 The stress-strain diagrams of the polyester P(Bu-BL) prepared in Example 3 and the polyester P(Ph-BL) prepared in Example 4.

[0098] Fig.17 This is the DMA spectrum of the polyester P(Bu-BL) prepared in Example 3.

[0099] Fig.18 This is the DMA spectrum of the polyester P (Ph-BL) prepared in Example 4.

[0100] Fig.19 This is a graph showing the hydrolysis mass change of the polyester P(Bu-BL) prepared in Example 3.

[0101] Fig. 20 This is a graph showing the hydrolysis mass change of the polyester P (Ph-BL) prepared in Example 4.

[0102] Fig.21 This is a comparison chart of the H NMR spectra of the polyester P (Ph-BL) prepared in Example 5 after degradation and recovery.

[0103] Fig. 22 This is a comparison chart of the H NMR spectra of the polyester P(Bu-BL) prepared in Example 6 after degradation and recovery.

[0104] Fig.23 The H NMR spectrum of the triblock copolymer P(Ph-BL)-b-PCL-bP(Ph-BL) prepared in Example 7 ( 1 1H NMR).

[0105] Fig.24 The carbon NMR spectrum of the triblock copolymer P(Ph-BL)-b-PCL-bP(Ph-BL) prepared in Example 7 (13 C NMR). DETAILED DESCRIPTION

[0106] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0107] Example 1

[0108] The specific steps are as follows:

[0109]

[0110] 3-Carbonyl-cyclobutanecarboxylic acid methyl ester (50 g, 0.390 mol, 1.0 equivalent) was added to a 2L round-bottom flask, dissolved in 600 mL of methanol, and sodium borohydride (8.86 g, 0.234 mol, 0.6 equivalent) was added in batches under an ice bath, and stirred for 30 min. The mixture was quenched with saturated ammonium chloride solution until neutral, and the methanol was spin-dried. The aqueous phase was extracted 3 times with dichloromethane, and the organic phase was washed once with saturated brine, dried over anhydrous sodium sulfate, and the solvent was spin-dried to obtain 40.5 g of the product with a yield of 80%, which was directly used in the next step reaction. 1 H NMR (400MHz, CDCl3) δ4.19(m,1H),3.69(s,3H),2.64-2.55(m,3H),2.23-2.13(m,2H).

[0111]

[0112] Under nitrogen protection and ice bath, add diisopropyl lithium amide tetrahydrofuran / n-hexane solution (2M, 254mL, 0.507mol, 2.2 equivalents) to a 1L three-necked flask, dissolve 3-hydroxy-cyclobutanecarboxylic acid methyl ester (30g, 0.231mol, 1.0 equivalent) prepared in the previous step in 290mL tetrahydrofuran, slowly add to the three-necked flask, stir for 10min, return to room temperature and stir for 1h, then slowly add 1-iodobutane, stir overnight. Add 2M HCl solution to quench, spin-dry tetrahydrofuran, extract with ethyl acetate 3 times, wash with water 1 time, wash with saturated brine 1 time, dry, spin-dry the solvent, and separate by column chromatography to obtain 22.6g of product with a yield of 53%. 1 H NMR(400MHz, CDCl3)δ4.27(qu,J=6.8Hz,1H),3.69(s,3H),2.38-2.27(m,4H),1.6 9-1.65(m,2H),1.28(qu,J=7.2Hz,2H),1.19-1.13(m,2H),0.88(t,J=7.2Hz,3H).

[0113]

[0114] The product prepared in the previous step (22.4 g, 0.121 mol, 1.0 equivalent) and 0.5 M NaOH solution (24 mL, 0.012 mol, 0.1 equivalent) were added to a 200 mL round-bottom flask, stirred, and then 5 M NaOH solution (24 mL, 0.121 mol, 0.1 equivalent) was added under ice bath, stirred for 30 min, returned to room temperature, and stirred for 2.5 h. 430 mL of concentrated hydrochloric acid was added under ice bath to acidify, the aqueous phase was extracted with ether 3 times, dried, and the solvent was spin-dried to obtain 19.7 g of product with a yield of 94%, which was directly used in the next step reaction. 1 H NMR (400MHz, CDCl3) δ4.30(qu,J=6.8Hz,1H),2.37(m,4H),1.72-1.68(m,2H),1.31(qu,J=7.2Hz,2H),1.27-1.22(m,2H),0.90(t,J=7.2Hz,3H).

[0115]

[0116] Under nitrogen protection, the product of the previous step (22.7 g, 0.132 mol, 1.0 equivalent) was added to a 500 mL three-necked flask, dissolved in 230 ml of anhydrous dichloromethane, EDCI (27.8 g, 0.145 mol, 1.1 equivalent), HOBt (19.6 g, 0.145 mol, 1.1 equivalent) and anhydrous triethylamine (20.2 mL, 0.145 mol, 1.1 equivalent) were added thereto, and stirred at room temperature for 30 min. The mixture was quenched with saturated saline, the organic phase was separated, the aqueous phase was extracted 3 times with dichloromethane, the organic phase was washed with water 2 times, washed with saturated saline once, dried, the solvent was spin-dried, and separated by column chromatography to obtain 13.2 g of the target product [2.1.1] bridged ring lactone Bu-BL monomer with a yield of 65%. 1 H NMR (400MHz, CDCl3) δ4.84 (s, 1H), 2.44-2.38 (m, 2H), 2.33-2.27 (m, 2H), 1.73-1.69 (m, 2H), 1.38-1.33 (m, 4H), 0.91 (t, J = 7.2Hz, 3H). 13 C NMR (101MHz, CDCl3) δ179.1,75.8,55.1,50.9,27.6,26.9,22.9,13.9.HRMS-ESI: calculated m / z 154.0994; found m / z155.1067[M+H + ]. 1 H NMR and 13 C NMR spectrum Figure 1 and 2shown.

[0117] Example 2

[0118] The specific steps are as follows:

[0119]

[0120] Triphosgene (25 g, 0.084 mol, 0.34 equivalent) was added to a 1L round-bottom flask and dissolved in 70 mL of dichloromethane. Ethanol (11.4 g, 0.248 mol, 1.0 equivalent) and triethylamine (34.4 mL, 0.248 mol, 1.0 equivalent) were dissolved in 140 mL of dichloromethane and slowly added to the flask. The mixture was reacted for 1 h, returned to room temperature, and reacted for 2 h. The mixture was washed with water 3 times, dried, and the solvent was removed by atmospheric distillation to obtain 18.8 g of the product with a yield of 70%. 1 H NMR (400MHz, CDCl3): δ4.38 (q, J=7.2Hz, 2H), 1.39 (t, J=7.2Hz, 3H).

[0121]

[0122] Under nitrogen protection and ice bath, add isopropyl magnesium chloride tetrahydrofuran solution (2M, 194mL, 0.388mol, 2.2 equivalents) to a 1L three-necked flask, dissolve phenylacetic acid (24g, 0.176mol, 1.0 equivalents) in 100ml tetrahydrofuran, slowly add to the three-necked flask, then add epichlorohydrin (30.3g, 0.317mol, 1.8 equivalents), stir for 5min, return to room temperature and stir for 45min, then add more isopropyl magnesium chloride tetrahydrofuran solution (2M, 176mL, 0.353mol, 2.0 equivalents), heat to 60℃ for 14h. Slowly add dilute hydrochloric acid solution to quench under ice bath, spin off tetrahydrofuran, extract with ethyl acetate 3 times, wash the organic phase with water and saturated brine, dry, spin dry the solvent, add toluene, precipitate crystals at low temperature, filter to obtain 20.3g product, yield 60%. 1 H NMR (400MHz, DMSO-d6): δ12.23(br,1H),7.39-7.22(m,5H),3.85(qu,J=7.2Hz,1H),3.34(s,1H),2.77-2.72(m,2H),2.50(m,2H).

[0123]

[0124] Under nitrogen protection, the product of the previous step (20 g, 0.104 mol, 1.0 equivalent) was added to a 2L three-necked flask, dissolved in 440 mL of anhydrous tetrahydrofuran, and then anhydrous triethylamine (16 mL, 0.114 mol, 1.1 equivalent) was added, and stirred to dissolve at room temperature; under an ice bath, ethyl chloroformate (11.3 g, 0.104 mol, 1.0 equivalent) was added, stirred for 1 h, returned to room temperature and stirred for 20 h; the solvent was dried, a small amount of water was added to dissolve, extracted with ethyl acetate, dried, the solvent was dried, and analyzed by column chromatography to obtain 16.6 g of the target product [2.1.1] bridged ring lactone Ph-BL monomer with a yield of 92%. 1 H NMR (400MHz, CDCl3) δ7.42-7.30(m,5H),4.97(s,1H),2.88(m,2H),2.71(m,2H). 13 C NMR (101MHz, CDCl3) δ176.9,134.2,128.6,128.0,126.9,75.2,57.5,52.6.HRMS-ESI: calculated m / z 174.0681; found m / z 175.0753[M+H + ]. 1 HNMR and 13 CNMR spectrum Figure 3 and Figure 4 shown.

[0125] Example 3

[0126] The specific steps are as follows:

[0127]

[0128] In an argon atmosphere glove box, add 10 mg Zn1 catalyst and 1135 μL toluene to a 5 mL reaction bottle to prepare a catalyst solution for use. Add 100 mg [2.1.1] bridged ring lactone monomer and 470 μL toluene to another 5 mL reaction bottle, and take 80 μL of the catalyst solution and add it to the stirring monomer solution. At this time, the molar ratio of monomer / catalyst is 500 / 1, the monomer concentration is 1.0 mol / L, and the polymerization temperature is room temperature. Samples are taken during the polymerization and analyzed by nuclear magnetic resonance hydrogen spectroscopy ( 1 After the polymerization was completed, the reaction was quenched with a chloroform solution of benzoic acid (10 mg / mL), and the polymer was poured into ice methanol to precipitate. The polymer was washed with ice methanol for several times and dried in a vacuum oven at 60°C until the weight did not change.

[0129] The present invention performs nuclear magnetic resonance hydrogen spectrum detection on the obtained reaction solution, and the result shows that the monomer conversion rate is>99%; the dried polymer is subjected to nuclear magnetic resonance detection, and it is confirmed that it is a polyester P (Bu-BL) with a four-membered ring in the main chain. 1 H NMR and 13 CNMR spectrum Figure 5 and Figure 6 shown.

[0130] The present invention adopts gel permeation chromatography (GPC) to analyze the molecular weight of the polymer, using chloroform as the mobile phase, the flow rate is 1mL / min, and polystyrene as the standard to make a standard curve. The results show that the number average molecular weight is M n =109kg / mol, dispersion D = 1.06, GPC curve as Fig. 9 shown.

[0131] The present invention adopts matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) to analyze the terminal groups of the polymer in this embodiment. According to the mass-to-charge ratio of the molecular ion peak and the fitting curve of the repeating unit, it can be obtained that the polymer is a linear polymer with terminal groups of isopropoxy / hydrogen.

[0132] Example 4

[0133] The specific steps are as follows:

[0134]

[0135] In an argon atmosphere glove box, add 10 mg Y1 catalyst and 1540 μL toluene to a 5 ml reaction bottle to prepare a catalyst solution for use. Add 120 mg [2.1.1] bridged lactone monomer and 544 μL toluene to another 5 mL reaction bottle, and add 54 μL of catalyst solution to the stirring monomer solution. At this time, the molar ratio of monomer / catalyst is 500 / 1, the monomer concentration is 1.0 mol / L, and the polymerization temperature is room temperature. Samples are taken during the polymerization and analyzed by nuclear magnetic resonance hydrogen spectroscopy ( 1 After the polymerization was completed, the reaction was quenched with a chloroform solution of benzoic acid (10 mg / mL), and the polymer was poured into ice methanol to precipitate. The polymer was washed with ice methanol for several times and dried in a vacuum oven at 60°C until the weight did not change.

[0136] The present invention performs nuclear magnetic resonance hydrogen spectrum detection on the obtained reaction solution, and the result shows that the monomer conversion rate is 95%; the dried polymer is subjected to nuclear magnetic resonance detection, and it is confirmed that it is a polyester P (Ph-BL) with a four-membered ring in the main chain. 1 H NMR and 13 CNMR spectrum Figure 7 and Figure 8 shown.

[0137] The present invention adopts GPC to analyze the molecular weight of the polymer, using chloroform as the mobile phase, the flow rate is 1mL / min, and polystyrene as the standard to make a standard curve. The results show that the number average molecular weight is M n =486kg / mol, dispersion GPC curve Fig.10 shown.

[0138] The present invention uses MALDI-TOF MS to analyze the end groups of the polymer in this embodiment. According to the mass-to-charge ratio of the molecular ion peak and the fitting curve of the repeating unit, it can be obtained that the polymer is a linear polymer with an end group of Me3SiCH2 / H.

[0139] Performance Test:

[0140] The present invention uses thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to measure the thermal decomposition temperature, glass transition temperature, melting point and crystallization temperature of the polymers P(Bu-BL) and P(Ph-BL) in Examples 3 and 4. Fig.11 and Fig.12 As shown, the starting decomposition temperature of P(Bu-BL) is T d,5％ =380℃, glass transition temperature T g =21°C (second heating), melting point T m =99°C (first heating); and Fig.13 and Fig.14 As shown, the starting decomposition temperature of P(Ph-BL) is T d,5％ =376℃, glass transition temperature T g =109℃(second heating), melting point T m =241°C (second heating). The results show that both polymers have high thermal stability and crystallinity, among which the value of the starting decomposition temperature is higher than any other recyclable polyester reported in the literature, so that the polymer has a processing window greater than 100°C and has excellent processing performance; at the same time, changing the side chain substituents can easily adjust the thermal properties of the polymer.

[0141] The present invention uses X-ray diffraction (XRD) to verify the crystallinity of the polymer and calculate the crystallinity, such as Fig.15 As shown, the crystallinity of the polymer P(Bu-BL) in Example 3 is 35%, and the crystallinity of the polymer P(Ph-BL) in Example 4 is 42%.

[0142] The present invention tests the mechanical properties of the polymers in Example 3 and Example 4. Using the same polymerization steps and changing the monomer / catalyst ratio, P(Bu-BL) with a molecular weight of 309 kg / mol and P(Ph-BL) with a molecular weight of 410 kg / mol are prepared respectively. The two polymer films are prepared by solvent evaporation method and cut into dog-bone-shaped strips for uniaxial tensile test. The stress-strain curves are shown in FIG. Fig.16 As shown, the yield stress σ of P(Bu-BL) B =16.4MPa, tensile strength σ B =25.3MPa, elongation at break ε B =500%, Young's modulus E = 446MPa, is a strong and tough material, its thermodynamic properties are similar to those of commercial plastic low-density polyethylene (T m ~110℃,E~300MPa,σ y ~8.0MPa,σ B ~20MPa,ε B ~500%) is equivalent to or even better than low-density polyethylene; while the tensile strength of P(Ph-BL)σ B = 30.6MPa, elongation at break 4.9%, Young's modulus 1.56GPa, is a hard and brittle material, and its thermodynamic properties are similar to those of commercial plastic polystyrene (T g ~100℃,T m ~240℃,σ B ~42MPa,ε B ~5%, E~3.6GPa). Therefore, P(Bu-BL) and P(Ph-BL) are expected to become potential substitutes for non-degradable commercial plastics low-density polyethylene and polystyrene.

[0143] The present invention further characterizes the mechanical properties of the polymer using dynamic mechanical analysis (DMA), such as Fig.17 As shown in Figure 2, at 25°C, the storage modulus of P(Bu-BL) is 1.31 GPa, and the loss modulus is 147 MPa. According to the vertex value of tanδ, T g is 135℃; Fig.18 As shown, the storage modulus of P(Ph-BL) is 2.63 GPa, the loss modulus is 84 MPa, and T g is 42°C. Above T g After that, the storage modulus of the two decreased by an order of magnitude, but was still higher than 100MPa, maintaining good elasticity.

[0144] The present invention tests the hydrolysis resistance of the polymers in Example 3 and Example 4 by immersing the polymer films of the two in acidic, alkaline and neutral aqueous solutions, respectively. Fig.19 and Fig. 20As shown, after 60 days, there is no obvious quality change. It has excellent anti-hydrolysis properties and is suitable for various outdoor humid environments.

[0145] The rigid four-membered ring structure on the main chain gives the polymer excellent thermal properties, mechanical properties and hydrolysis resistance, while the presence of ester bonds makes the polymer degradable and can be recycled to obtain monomers.

[0146] Example 5

[0147]

[0148] The specific steps are as follows:

[0149] Solution degradation recovery: In a glove box, add 10.8 mg Y1 and 20 mg polymer P (Ph-BL) to a 10 mL Schlenk tube, then add 2.9 mL toluene (0.1 M). After sealing, take out the glove box, heat at 130 °C, react for 29 h, and only 31% of the polymer is degraded to monomer.

[0150] Bulk melt degradation recovery: In a glove box, add 1.13 mg Y(CH2SiMe3)3(THF)2 (2 mol%) and 20 mg polymer P(Ph-BL) into a 10 mL Schlenk tube. After sealing, take out the glove box, heat at 250 °C, and react for 19 h. The polymer is efficiently degraded to monomers with a conversion rate of >98%. See Fig.21 .

[0151] Example 6

[0152]

[0153] The specific steps are as follows:

[0154] Bulk melt degradation recovery: In a glove box, add 1.61 mg La1 (2 mol%) and 20 mg polymer P (Bu-BL) to a 10 mL Schlenk tube. After sealing, take out the glove box, heat at 260 ° C, and react for 8 h. The polymer is efficiently degraded to monomers with a conversion rate of >98%. See Fig. 22 .

[0155] Example 7

[0156]

[0157] The specific steps are as follows:

[0158] Preparation of triblock copolymers by one-pot method: In a glove box with argon atmosphere, add 8 mg Y2 catalyst and 1111 μL toluene to a 5 mL reaction bottle to prepare a catalyst solution for use, add 8 mg 1,4-butanediol and 800 μL toluene to another 5 mL reaction bottle, take 44 μL of 1,4-butanediol toluene solution and add it to the Y2 catalyst solution, mix for 10 minutes, and in situ alcoholysis occurs; add 60 mg [2.1.1] bridged ring lactone monomer Ph-BL and 39 mg ε-caprolactone to a third 5 mL reaction bottle, dissolve in 288 μL toluene, take 400 μL of the mixed solution of catalyst and initiator and add it to the stirring monomer solution. At this time, the molar ratio of Ph-BL / ε-caprolactone / catalyst / initiator is 200 / 200 / 2 / 1, and the polymer temperature is room temperature. Samples are taken during the polymerization process and analyzed by nuclear magnetic resonance hydrogen spectrum ( 1 After the polymerization was completed, the reaction was quenched with a chloroform solution of benzoic acid (10 mg / mL), and the polymer was poured into ice methanol to precipitate. The polymer was washed with ice methanol for several times and dried in a vacuum oven at 60°C until the weight did not change.

[0159] The present invention performs nuclear magnetic resonance hydrogen spectrum detection on the obtained reaction solution, and the result shows that the conversion rate of Ph-BL is 87%, and the conversion rate of ε-caprolactone is 97%. The dried polymer is subjected to nuclear magnetic resonance detection, and it is confirmed to be a triblock copolymer of P(Ph-BL)-b-PCL-bP(Ph-BL). 1 H NMR and 13 C NMR spectrum Fig.23 and Fig.24 shown.

[0160] The present invention adopts GPC to analyze the molecular weight of the polymer, using chloroform as the mobile phase, the flow rate is 1mL / min, and polystyrene as the standard to make a standard curve. The results show that the number average molecular weight is M n =60.7kg / mol, dispersion degree D=1.25.

[0161] The above descriptions are only some implementation cases of the present invention and are not intended to limit the present invention. Any modifications, substitutions, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A [2.1.1] bridged lactone monomer, the general structural formula of which is shown in Formula I: In formula I, R is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl; the substituent in R is alkyl, alkoxy and / or halogen.

2. The [2.1.1] bridged lactone monomer according to claim 1, characterized in that R is selected from the following structures: Wherein, n is an integer greater than or equal to 0; X represents a halogen selected from F, Cl, Br, and I.

3. The method for preparing the bridged lactone monomer according to claim 1 [2.1.1], comprising: 1) When R is an alkyl group, the general reaction formula is as follows: 1a) dissolving 3-carbonyl-cyclobutanecarboxylic acid methyl ester in an organic solvent, adding a reducing agent under an ice bath, stirring, quenching after the reaction, extracting, washing, drying, and spinning the solvent to obtain 3-hydroxy-cyclobutanecarboxylic acid methyl ester; 1b) In an ice bath, slowly add an organic solution of methyl 3-hydroxy-cyclobutanecarboxylate to a non-nucleophilic strong base solution, stir, return to room temperature and stir for a period of time, then add alkyl iodide dropwise, stir overnight; add an acid solution to quench, extract, wash, and spin-dry the solvent to obtain intermediate a; 1c) mixing intermediate a with a strong base solution, stirring to react, adding an acid solution to quench after the reaction is completed, extracting, washing, drying, and spinning the solvent to obtain intermediate b; 1d) dissolving the intermediate b in an organic solvent, adding a condensing agent and HOBt, stirring for reaction, extracting, washing, and drying to obtain the target monomer alkyl-substituted [2.1.1] bridged ring lactone; 2) When R is an aromatic group, the general reaction formula is as follows: 2a) dissolving triphosgene in an organic solvent, placing it in an ice bath, slowly adding a mixed organic solution of ethanol and a nucleophilic agent thereto, reacting under an ice bath, then warming to room temperature to react, then washing with water, drying, and removing the solvent to obtain ethyl chloroformate; 2b) adding an organic solution of arylacetic acid and epichlorohydrin to the Grignard reagent under ice bath conditions, stirring, reacting at room temperature, then adding more Grignard reagent, heating to 50-60° C. for reaction; after the reaction is completed, adding an acid solution for quenching, extracting, washing, drying, spinning the solvent to dryness, adding a poor solvent for crystallization, and obtaining an intermediate c; 2c) The intermediate c is dissolved in an organic solvent, an acid binding agent is added thereto, the mixture is placed in an ice bath, and then ethyl chloroformate is added. The mixture is reacted for a period of time, the temperature is restored to room temperature, and the reaction is continued. After the reaction is completed, the mixture is extracted, washed, dried, and the solvent is dried by spin drying to obtain the target monomer aromatic-substituted [2.1.1] bridged ring lactone.

4. The method for preparing a bridged lactone monomer [2.1.1] according to claim 3, characterized in that: In step 1a), the organic solvent is selected from one or more of methanol, ethanol, N,N-dimethylformamide, and tetrahydrofuran; the reducing agent is selected from one or more of sodium borohydride, methylmagnesium bromide, phenylmagnesium bromide, and benzylmagnesium bromide; in step 1b), the organic solvent is selected from one or more of tetrahydrofuran, ether, and n-hexane; the strong base in the non-nucleophilic strong base solution is one of lithium diisopropylamide and lithium bistrimethylsilylamide; the acid solution is one of 1-5M hydrochloric acid and sulfuric acid solution; in step 1 c) the strong alkali solution is selected from one of sodium hydroxide, lithium hydroxide and potassium hydroxide solutions; the acid solution is one of 1-5M hydrochloric acid and sulfuric acid solution; the organic solvent in step 1d) is selected from one of dichloromethane, chloroform, tetrahydrofuran, ether, toluene and ethyl acetate; the condensing agent is one of EDCI (1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride), DCC (1,3-dicyclohexylcarbodiimide) and DIC (N,N-diisopropylcarbodiimide); The organic solvent in step 2a) is selected from one or more of dichloromethane, chloroform, tetrahydrofuran, ether, and toluene; the nucleophilic reagent is selected from one of triethylamine, pyridine, N,N-diisopropylethylamine and dimethylformamide; the organic solvent in step 2b) is selected from one or more of dichloromethane, tetrahydrofuran, toluene, and ethyl acetate; the Grignard reagent is selected from one of isopropylmagnesium chloride, methylmagnesium chloride, and phenylmagnesium chloride; the acid solution is one of 1-5M hydrochloric acid and sulfuric acid solution; the acid binding agent in step 2c) is one of triethylamine, n-butylamine, diethylmethylamine, and pyridine; the organic solvent is selected from one or more of dichloromethane, chloroform, tetrahydrofuran, ether, and toluene.

5. A polyester having a four-membered ring in the main chain, the general structural formula of which is shown in Formula II: In formula II, n is the degree of polymerization; R is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl; the substituent in R is alkyl, alkoxy and / or halogen.

6. The polyester according to claim 5, characterized in that R is selected from the following structures: Wherein, n is an integer greater than or equal to 0; X represents a halogen selected from F, Cl, Br, and I.

7. The method for preparing the polyester according to claim 5, comprising subjecting the bridged lactone monomer [2.1.1] of formula I to a ring-opening polymerization reaction in an organic solvent in the presence of a metal catalyst to obtain the polyester of formula II; in, n is the degree of polymerization; R is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl; the substituent in R is alkyl, alkoxy and / or halogen.

8. The preparation method according to claim 7, characterized in that: The metal catalyst is selected from one of the following compounds:

9. The preparation method according to claim 8, characterized in that: The polyester shown in formula II is a linear polymer. Under the catalysis of metal catalyst Y1 or Zn1, or under the co-catalysis of metal catalyst La1 or Y2 and initiator, the [2.1.1] bridged ring lactone monomer shown in formula I undergoes ring-opening polymerization, wherein the initiator is an alcohol compound.

10. The preparation method according to claim 8, characterized in that: The polyester shown in formula II is a cyclic polymer. t Under the catalysis of BuOK, the bridged lactone monomer [2.1.1] shown in formula Ⅰ undergoes a ring-opening polymerization reaction.

11. A method for recovering a polymer, wherein the polymer is a polyester represented by formula II, wherein the polymer and a catalyst are mixed into a solution and heated, or the polymer and a catalyst are mixed and heated to a molten state to achieve conversion of the polymer into a monomer; in, n is the degree of polymerization; R is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl; the substituent in R is alkyl, alkoxy and / or halogen; the catalyst is selected from Sn(Oct)2, ZnCl2, YCl3, LaCl3, TBD, DMAP, t BuOK, Y1, Y2, Zn1, La1 and Y(CH2SiMe3)3(THF)2, the solvent used is toluene, xylene and 1,2-dichlorobenzene; wherein Y1, Y2, Zn1, La1 and t The structure of BuOK is as follows:

12. A recyclable polyester, the general structural formula of which is shown in Formula III: In formula III, n and m are the degree of polymerization; x is an integer greater than or equal to 1; R is hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, and the substituent in R is alkyl, alkoxy and / or halogen; R 1 It is one or more of hydrogen, C1-C12 alkyl, C1-C12 alkoxy, halogen, and C6-C12 aryl.

13. The recyclable polyester according to claim 12, characterized in that R is selected from the following structures: Wherein, n is an integer greater than or equal to 0; X represents a halogen selected from F, Cl, Br, and I.

14. The method for preparing the recyclable polyester according to claim 12, wherein the reaction formula is as follows: The preparation is carried out by one-pot feeding or sequential feeding, wherein: One-pot method: Mix the bridged lactone monomer [2.1.1] shown in formula I with the second lactone monomer, add a metal catalyst and an initiator, and carry out a ring-opening copolymerization reaction in an organic solvent to obtain a random copolymer or block copolymer shown in formula III; Sequential addition: a lactone monomer is first mixed with a metal catalyst and an initiator in an organic solvent to generate a first-stage homopolymer, and then a second lactone monomer is added to the system to generate a second-stage polymer to obtain a block copolymer shown in formula III.

15. The preparation method according to claim 14, characterized in that: The metal catalyst is selected from one of the following compounds: The initiator is an alcohol compound; the organic solvent is a combination of one or more of dichloromethane, chloroform, toluene and tetrahydrofuran; and the polymerization reaction is carried out under an inert gas atmosphere.

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