A pure bio-based block copolymer and its preparation method

Abstract

The present invention discloses a pure bio-based block copolymer and a preparation method thereof. The pure bio-based block copolymer is shown in Formula I. The preparation method of the block copolymer is to use a lactone monomer as a reaction substrate, use the compound shown in Formula II and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene as catalysts, and use an organic alcohol as an initiator to carry out a ring-opening polymerization reaction. In the preparation process provided by the present invention, the two catalysts act synergistically. In the presence of the initiator alcohol, the self-polymerization and copolymerization of the lactone monomer are catalyzed to obtain copolyesters with different components. According to different polymerization reaction conditions, polyester products with adjustable structure, controllable molecular weight, and narrow molecular weight distribution can be obtained. The preparation process provided by the present invention also has the characteristics of simple process, low cost, high reaction rate, process controllability, narrow molecular weight distribution of the product, etc., and both bulk polymerization and solution polymerization can be implemented.

Description

Technical Field

[0001] The present invention belongs to the fields of green catalytic synthesis and polymer chemical materials, and particularly relates to a thioamide-based benzimidazole catalyst and its application in pure bio-based block copolymers. Background Art

[0002] Thermoplastic elastomers have characteristics such as good elasticity and reprocessability, and are widely used in hot melt pressure-sensitive adhesives, automotive parts, medical devices and other fields. Currently, common commercial thermoplastic elastomers include polystyrene-b-polybutadiene-b-polystyrene and polystyrene-b-polyisoprene-b-polystyrene. Although these materials have wide applications, they rely on non-renewable raw materials and cannot be degraded in the natural environment after being discarded. Therefore, the preparation of sustainable bio-based thermoplastic elastomers using safe and non-toxic biomass-based raw materials has attracted increasing attention.

[0003] L-lactide is derived from plants such as sugarcane, and polylactic acid obtained by ring-opening polymerization of it is a completely biodegradable polyester material. Hillmyer et al. reported the synthesis of poly(lactic acid)-b-poly(β-methyl-δ-valerolactone)-b-poly(lactic acid) triblock copolymer, and the obtained triblock copolymer exhibited the properties of thermoplastic elastomers and had relatively high mechanical strength and elongation at break. However, β-methyl-δ-valerolactone as a synthetic raw material is not a commercial monomer, and its synthesis steps are cumbersome and complex, making it difficult to carry out large-scale industrial production. Propyl-ε-caprolactone (ε-prCL) is a six-membered ring lactone with a propyl substitution at the ε-position, and is one of the depolymerization products of lignin bio-oil, which consists of hundreds of phenolic and cyclic aromatic compounds, and the products vary due to different raw material types, depolymerization methods, heating rates, reaction temperatures and catalysts. The chemical route proposed by Roman-Leshkov et al.: cresol separated from lignin pyrolysis oil is hydrogenated to form methyl-cyclohexanone, and then undergoes Baeyer-Villiger oxidation (BVO) to form methyl-ε-caprolactone. These combined reactions provide the possibility of downstream applications for lignin-derived alkylphenols, and can produce alkyl caprolactones with high net yields and high selectivities. Conventional linear-chain poly(ε-caprolactone) (PCL) is a semi-crystalline material, and the ester part in the polymer backbone endows biodegradability, and it can be mixed and copolymerized with other polymers to improve its properties. Branched poly(methyl-ε-caprolactone) (PMCL) and caprolactones containing other alkyl groups such as polypropyl-ε-caprolactone (PprCL) also benefit from this, but the addition of branched chains will result in the formation of amorphous materials with a low glass transition temperature (Tg≈-60 °C), presenting a rubber state at room temperature and expected to be used as the soft segment of thermoplastic elastomers.

[0004] In view of this, the present invention provides a method for preparing a pure bio-based copolyester by the selective ring-opening copolymerization of a monomer propyl-ε-caprolactone derived from lignin pyrolysis oil and lactide derived from cellulose. The catalysts mainly used in the industrial production of such copolymers are tin-based catalysts. Although tin-based catalysts have very high catalytic activity, they are biotoxic and prone to cause health risks when remaining in the human body. Therefore, it is necessary to seek a catalyst with low toxicity or no toxicity to replace tin-based catalysts. Acid-base pair catalysts are a new type of catalyst that has emerged in recent years, with characteristics such as high activity, strong controllability, and easy regulation of polymerization, and has been widely studied at home and abroad. Therefore, compared with the methods reported in the past, the method provided by the present invention has the following advantages: 1) The catalyst used has low toxicity and is easy to remove from the product. Biological experiments show that the obtained product has no obvious cytotoxicity and can be used in the biomedical field; 2) The catalytic system used has high selectivity and can achieve the selective ring-opening polymerization of propyl-ε-caprolactone during the copolymerization process to obtain linear copolyester molecules; 3) The monomer conversion rate is high and the atom economy is good. Among them, propyl-ε-caprolactone and L-lactide can be completely converted during the polymerization process; 4) The adjustable range of the proportion of propyl-ε-caprolactone structural units in the obtained copolyester is wide, which can vary from 6 to 92 mol%, and can better regulate the physical properties of the obtained copolyester. Summary of the Invention

[0005] Object of the Invention: The technical problem to be solved by the present invention is to provide a pure bio-based block copolymer in view of the deficiencies of the prior art.

[0006] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned pure bio-based block copolymer.

[0007] Another technical problem to be solved by the present invention is to provide a thioamide-based benzimidazole catalyst.

[0008] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned thioamide-based benzimidazole catalyst.

[0009] To solve the above first technical problem, the present invention discloses a pure bio-based block copolymer, which is a linear copolymer obtained by copolymerizing propyl-caprolactone (monomer A) and lactide (monomer B) as monomers, and the structural formula of the copolymer is shown in Formula I.

[0010]

[0011] Among them, R1 is selected from alkyl groups with straight-chain, branched-chain or cyclic structures of C1-C10, preferably p-xylene glycol group, butyl group or benzyl group, and preferably benzyl group; n≥1, m≥1.

[0012] Among them, the number-average molecular weight of the block copolymer is 1000 to 20000 g / mol, preferably 2000 to 20000 g / mol, preferably 4000 to 20000 g / mol, preferably 7000 to 20000 g / mol, preferably 9000 to 20000 g / mol, preferably 9000 to 18000 g / mol, preferably 9000 to 16000 g / mol, preferably 11000 to 16000 g / mol, preferably 13000 to 16000 g / mol, preferably 13000 to 15000 g / mol.

[0013] Among them, the distribution index of the block copolymer is 1.15 to 1.35, preferably 1.15 to 1.30, preferably 1.15 to 1.23, preferably 1.18 to 1.23.

[0014] Among them, the glass transition temperature of the block copolymer is -50 to -80 °C, preferably -60 to -70 °C, preferably -65 °C.

[0015] To solve the above-mentioned second technical problem, the present invention discloses a method for preparing a block copolymer, using a lactone monomer as a reaction substrate, a compound shown in Formula II and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene as binary co-catalysts, and an organic alcohol as an initiator to carry out ring-opening polymerization reaction to prepare a block copolymer;

[0016]

[0017] Among them, R1 and R2 are each independently selected from hydrogen, an electron-withdrawing group, an alkyl group or an alkoxy group.

[0018] Among them, the lactone monomer is any one or a combination of several of glycolide, lactide, butyrolactone, valerolactone, caprolactone, propyl-caprolactone, heptalactone, octalactone, trimethylene carbonate and 15-membered ring lactone, preferably any one or a combination of several of glycolide, lactide, butyrolactone, valerolactone, caprolactone, propyl-caprolactone, heptalactone and octalactone, preferably any one or a combination of several of glycolide, lactide, butyrolactone, valerolactone, caprolactone and propyl-caprolactone, preferably propyl-caprolactone and / or lactide, preferably propyl-caprolactone, or a combination of propyl-caprolactone (pr-CL) and lactide (δ-VL).

[0019] In some embodiments, the lactone monomer is propyl-caprolactone, and the resulting product is a homopolymer P(pr-Cl), and the molecular weight distribution index of the resulting product is only 1.28 to 1.34, respectively; in some embodiments, the lactone monomer is a combination of propyl-caprolactone (pr-CL) and lactide (δ-VL), and the resulting copolymer is the copolymer shown in Formula I, and the molecular weight distribution index of the resulting copolymer is only 1.15 to 1.35, preferably 1.15 to 1.30, preferably 1.15 to 1.23, preferably 1.18 to 1.23.

[0020] Among them, in the compound shown in Formula II, the electron-withdrawing group is selected from a halogen atom, trifluoromethyl or nitro, preferably a halogen atom or trifluoromethyl, preferably fluorine or trifluoromethyl. Among them, the alkyl group is selected from a C1-C10 straight-chain alkyl group or branched-chain alkyl group, preferably a C1-C5 straight-chain alkyl group or branched-chain alkyl group. Among them, the alkoxy group is selected from a C1-C10 straight-chain alkoxy group or branched-chain alkoxy group, preferably a C1-C5 straight-chain alkoxy group or branched-chain alkoxy group, preferably a C1-C3 straight-chain alkoxy group or branched-chain alkoxy group, preferably a methoxy group. The compound shown in Formula II is preferably any one of the following Compounds II-1 to II-2.

[0021]

[0022] Among them, the molar ratio of the lactone monomer to the catalyst is 1:35 to 65, preferably 1:40 to 60, preferably 1:45 to 55, preferably 1:48 to 52, preferably 1:50.

[0023] Among them, the molar ratio of the compound shown in Formula II to 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene is 1:0.5 to 1.5, preferably 1:0.7 to 1.3, preferably 1:0.8 to 1.2, preferably 1:0.9 to 1.1, preferably 1:1.

[0024] Among them, the organic alcohol is a C1-C10 straight-chain, branched-chain or cyclic organic alcohol, preferably a C1-C10 straight-chain, branched-chain or cyclic monohydric alcohol, dihydric alcohol, trihydric alcohol or polyhydric alcohol, preferably benzyl alcohol and / or p-xylene glycol, preferably benzyl alcohol.

[0025] Among them, the molar ratio of the lactone monomer to the organic alcohol is 50 to 115:1, preferably 50:1.

[0026] Among them, the reaction is carried out without adding a solvent or adding an organic solvent; the organic solvent is toluene and / or tetrahydrofuran.

[0027] Among them, the reaction temperature is 20 to 100 °C, preferably 25 to 80 °C, more preferably 25 to 50 °C.

[0028] Among them, after the reaction is completed, an acidic substance is added to terminate the reaction, and the reaction mixture is added to methanol for sedimentation to obtain the product; the acidic substance is preferably a mixed solution of benzoic acid and dichloromethane.

[0029] To solve the above-mentioned third technical problem, the present invention discloses a compound (thioamide-based benzimidazole catalyst) represented by Formula II,

[0030]

[0031] wherein, R1 and R2 are each independently selected from hydrogen, an electron-withdrawing group, an alkyl group or an alkoxy group; and R1 and R2 are not simultaneously trifluoromethyl;

[0032] Preferably, the electron-withdrawing group is selected from a halogen atom, trifluoromethyl or nitro, preferably a halogen atom or trifluoromethyl, more preferably fluorine or trifluoromethyl;

[0033] Preferably, the alkyl group is selected from a straight-chain alkyl group or a branched-chain alkyl group having 1 to 10 carbon atoms, preferably a straight-chain alkyl group or a branched-chain alkyl group having 1 to 5 carbon atoms;

[0034] Preferably, the alkoxy group is selected from a straight-chain alkoxy group or a branched-chain alkoxy group having 1 to 10 carbon atoms, preferably a straight-chain alkoxy group or a branched-chain alkoxy group having 1 to 5 carbon atoms, more preferably a straight-chain alkoxy group or a branched-chain alkoxy group having 1 to 3 carbon atoms, most preferably methoxy;

[0035] Preferably, the compound represented by Formula II is the following Compound II-2;

[0036]

[0037] To solve the above-mentioned fourth technical problem, the present invention discloses a preparation method of the above-mentioned thioamide-based benzimidazole catalyst.

[0038] As Figure 1 shown, the preparation method of the thioamide-based benzimidazole catalyst includes the following steps: (1) Dissolve 2-amino-5,6-dimethylbenzimidazole and N,N-diisopropylethylamine in THF, and then slowly dropwise add benzoyl chloride, stir and react, concentrate and dry to obtain a corresponding acylamino-imidazole mixture; (2) Reflux the corresponding acylamino-imidazole mixture and Lawesson's reagent in toluene, then evaporate to dryness, dissolve the residue in CH2Cl2, and the resulting solution is washed successively with water and brine, dried over MgSO4 and evaporated. Finally, it is purified by column chromatography to obtain a yellow solid, which is the thioamide-based benzimidazole catalyst.

[0039] In step (1), the molar ratio of 2-amino-5,6-dimethylbenzimidazole to benzoyl chloride is 1:1 to 2.

[0040] In step (2), the molar ratio of the corresponding acylamino-imidazole mixture to Lawesson's reagent is 1:1 to 2.

[0041] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0042] The present invention not only has good catalytic effect, but also has the characteristics of simple process compared with the traditional synthesis process. The traditional catalysts for synthesizing polyvalerolactone and polycaprolactone are metal catalysts and enzyme catalysts. However, the polymers synthesized by metal catalysts and enzyme catalysts often have disadvantages such as metal residues, reaction inactivity, uncontrollable polymer molecular weight, and wide molecular weight distribution. And the polymerization reaction needs to be carried out under conditions such as high temperature or bulk, resulting in low product performance and great limitations in industrial applications. While the present invention adopts a one-step one-pot process. In one reactor, thioamide benzimidazole and commercial base are used as a co-catalytic system to directly catalyze the ring-opening polymerization of monomers at room temperature, and copolyesters with controllable molecular weights are obtained. The molecular weight distribution indexes are only 1.28 - 1.34 and 1.15 - 1.35 respectively, and the monomer conversion rate of the polymer is 90 - 99%. It has high biosafety and has wide applications in the field of medical materials.

[0043] In the preparation process provided by the present invention, the two catalysts act synergistically. In the presence of the initiator alcohol, they catalyze the self-polymerization and copolymerization of lactone monomers to obtain copolyesters with different components. According to different polymerization reaction conditions, polyester products with adjustable structure, controllable molecular weight, and narrow molecular weight distribution can be obtained.

[0044] The preparation process provided by the present invention also has the characteristics of simple process, low cost, high reaction rate, process controllability, narrow molecular weight distribution of the product, etc., and both bulk polymerization and solution polymerization can be implemented. Description of the Drawings

[0045] The following further specifically describes the present invention in conjunction with the drawings and specific embodiments, and the above and / or other advantages of the present invention will become clearer.

[0046] Figure 1 It is the synthesis route diagram of the catalyst.

[0047] Figure 2 It is the 1H NMR spectrum of the homopolymer P(pr-Cl) in Example 7.

[0048] Figure 3 It is the 1H NMR spectrum of the copolymer P(pr-Cl-b-D-LA) in Example 8.

[0049] Figure 4 Gel Permeation Chromatography (GPC) chart of copolymer P(prCL)-b-PLA in Example 8.

[0050] Figure 5 TGA spectrum of copolymer P(prCL)-b-PLA in Example 9.

[0051] Figure 6 DSC spectrum of copolymer P(prCL)-b-PLA in Example 9. Detailed implementation manners

[0052] In the following examples, unless otherwise specified, the experimental methods are all conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial channels.

[0053] The structures of catalysts II-1 to II-2 described in the following examples are specifically shown as follows.

[0054]

[0055] The specific preparation method of propyl-caprolactone described in the following examples is (reference: Macromolecules. 2011; 44(1): 87-94.).

[0056] The molecular weight of the polymer described in the following examples can be calculated according to the following formula:

[0057] Mn = ([pr-CL]0 / [BnOH]0) × conv. × (M W of pr-CL) + (M W of BnOH)

[0058] Where, [pr-CL]0 is the initial molar input amount of the monomer, [BnOH]0 is the initial molar input amount of the initiator, conv. is the monomer conversion rate, M W of pr-CL is the molecular weight of the monomer, M W of BnOH is the molecular weight of the initiator.

[0059] Example 1

[0060] Weigh 2-amino-5,6-dimethylbenzimidazole (6 mmol, 0.798 g) in a 50 mL round-bottom flask and dissolve it in 30 mL of THF. Add N,N-diisopropylethylamine (12 mmol, 1.55 g) to the solution, and then slowly drip 10 mL of a THF solution of 3,5-bis(trifluoromethyl)benzoyl chloride (6.3 mmol, 1.742 g). Stir for 16 h. After the reaction is completed, concentrate and dry to obtain a mixture of benzoylamino-benzimidazole. React the corresponding mixture of benzoylamino-benzimidazole (1 mmol) and Lawesson's reagent (1 mmol) in toluene (15 mL) under reflux for 16 h under nitrogen and evaporate to dryness. Dissolve the residue in CH2Cl2 (50 mL), wash the resulting solution successively with water (1×30 mL) and brine (1×30 mL), dry with MgSO4, filter to obtain the crude product, wash it three times with anhydrous and anaerobic dichloromethane, place the precipitate in a vacuum oven to dry, and finally obtain catalyst II-1.

[0061] 1H NMR ((CD3)2SO, 295 K): δ = 2.33 (s, 6H), 7.43 (s, 2H), 8.22 (s, 1H), 8.92 (s, 2H), 13.49 (s, 2H); 13C NMR ((CD3)2SO, 295 K): δ = 19.9, 112.8, 123.3 (m), 123.4 (q, 1J = 272.9 Hz), 126.8, 128.0 (m), 129.7 (q, 2J = 32.5), 133.0, 145.9, 152.0, 195.2; ppm.

[0062] Example 2

[0063] Weigh 2-amino-5,6-dimethylbenzimidazole (6 mmol, 0.798 g) in a 50 mL round-bottom flask and dissolve it in 30 mL of THF. Add N,N-diisopropylethylamine (12 mmol, 1.55 g) to the solution, and then slowly drip 10 mL of a THF solution of 3-methoxybenzoyl chloride (6.3 mmol, 1.07 g). Stir for 16 h. After the reaction is completed, concentrate and dry to obtain a mixture of amido-imidazole. React the corresponding mixture of amido-imidazole (1 mmol) and Lawesson's reagent (1 mmol) in toluene (15 mL) under reflux for 16 h under nitrogen and evaporate to dryness. Dissolve the residue in CH2Cl2 (50 mL), wash the resulting solution successively with water (1×30 mL) and brine (1×30 mL), dry with MgSO4, filter to obtain the crude product, wash it three times with anhydrous and anaerobic dichloromethane, place the precipitate in a vacuum oven to dry, and finally obtain catalyst II-2.

[0064] 1H NMR ((CD3)2SO, 295K): δ = 2.32 (s, 6H), 3.81 (s, 3H), 7.02 (ddd, 3J = 8.3 Hz, 4J = 2.6 Hz, 4J = 1.1 Hz, 1H), 7.30 (t, 3J = 7.9 Hz, 1H), 7.39 (s, 2H), 7.89 (m, 2H), 13.42 ppm (s, 2H); 13C NMR ((CD3)2SO, 295K): δ = 19.9, 55.1, 112.6, 113.3, 115.9, 120.6, 126.8, 128.4, 132.5, 146.1, 152.7, 158.6, 200.6 ppm.

[0065] Example 3

[0066] 53.248 mg of catalyst II-1 (0.128 mmol) and 19.58 mg of MTBD (0.128 mmol) were pre-added to a Schlenk flask. 13.824 mg of benzyl alcohol (0.128 mmol) was dissolved in 2 ml of anhydrous toluene, stirred evenly and then 1000 mg of propyl - caprolactone (6.4 mmol) was added. The temperature was controlled at 30 °C and the reaction was carried out for 3 h. An excess of benzoic acid / dichloromethane solution was added to terminate the reaction, and then it was precipitated twice with cold anhydrous methanol and dried in vacuo to constant weight to obtain the finished product. The 1H NMR of the polymer is as Figure 2 shown.

[0067] Example 4

[0068] 53.248 mg of catalyst II-1 (0.128 mmol) and 19.58 mg of MTBD (0.128 mmol) were pre-added to a Schlenk flask. 13.824 mg of benzyl alcohol (0.128 mmol) was dissolved in 2 ml of anhydrous toluene, stirred evenly and then 1000 mg of propyl - caprolactone (6.4 mmol) was added. The temperature was controlled at 30 °C and the reaction was carried out for 3 h. It was transferred to a glove box and 921.6 mg of lactide (6.4 mmol) was further added, and the reaction was continued and monitored by NMR until the reaction was complete. Finally, an excess of benzoic acid / dichloromethane solution was added to terminate the reaction, and then it was precipitated twice with cold anhydrous methanol and dried in vacuo to constant weight to obtain the finished product. The 1H NMR of the polymer is as Figure 3 shown, and the GPC chromatogram is as Figure 4 shown.

[0069] Example 5

[0070] Pre-add 39.68 mg of catalyst II-2 (0.128 mmol) and 19.58 mg of MTBD (0.128 mmol) into a Schlenk flask. Dissolve 13.824 mg of benzyl alcohol (0.128 mmol) in 2 ml of anhydrous toluene, stir evenly and then add 1000 mg of propyl-caprolactone (6.4 mmol). Control the temperature at 30 °C and react for 3 h. Transfer it to a glove box and continue to add 921.6 mg of lactide (6.4 mmol). Continue the reaction and monitor by NMR until the reaction is complete. Finally, terminate the reaction with an excessive amount of benzoic acid / dichloromethane solution, and then precipitate twice with cold anhydrous methanol, and dry in vacuum to constant weight to obtain the finished product. Its TGA and DSC spectra are respectively as Figure 5 and Figure 6 shown. TGA indicates the thermal stability of the copolymer, with a 5% weight loss at 279 °C; DSC indicates the influence on the melting temperature (Tm) and crystallization temperature (Tc) of the copolymer after adding the LLA block. After adding the PLA segment, the Tm and Tc of the copolymer are increased.

[0071] Comparative Example 1: The same as Example 3, except that only MTBD is added and catalyst II-1 is not added.

[0072] Pre-add 19.58 mg of MTBD (0.128 mmol) into a Schlenk flask. Dissolve 13.824 mg of benzyl alcohol (0.128 mmol) in 2 ml of anhydrous toluene, stir evenly and then add 1000 mg of propyl-caprolactone (6.4 mmol). Control the temperature at 30 °C until the reaction is complete, add an excessive amount of benzoic acid / dichloromethane solution to terminate the reaction, and then precipitate twice with cold anhydrous methanol, and dry in vacuum to constant weight to obtain the finished product.

[0073] Comparative Example 2: The same as Example 3, adding MTBD and catalyst II-1, except that the monomer propyl-caprolactone is replaced by lactide.

[0074] Pre-add 53.248 mg of catalyst II-1 (0.128 mmol) and 19.58 mg of MTBD (0.128 mmol) into a Schlenk flask. Dissolve 13.824 mg of benzyl alcohol (0.128 mmol) in 6 ml of anhydrous toluene, stir evenly and then add 921.6 mg of lactide (6.4 mmol). Control the temperature at 30 °C until the reaction is complete, add an excessive amount of benzoic acid / dichloromethane solution to terminate the reaction, and then precipitate twice with cold anhydrous methanol, and dry in vacuum to constant weight to obtain the finished product.

[0075] Comparative Example 3: The same as Example 5, except that only MTBD is added and catalyst II-2 is not added.

[0076] 19.58 mg of MTBD (0.128 mmol) was pre-added into a Schlenk flask. 13.824 mg of benzyl alcohol (0.128 mmol) was dissolved in 2 ml of anhydrous toluene. After stirring evenly, 1000 mg of propyl - caprolactone (6.4 mmol) was added. The reaction was carried out at 30 °C for 3 h. Then it was transferred into a glove box and 921.6 mg of lactide (6.4 mmol) was added continuously. The reaction was monitored by NMR until it was complete. Finally, the reaction was terminated with an excessive amount of benzoic acid / dichloromethane solution, and then precipitated twice with cold anhydrous methanol and dried in vacuum to constant weight to obtain the finished product.

[0077] The results of the above Examples 3 - 5 and the corresponding comparative examples are shown in Table 1.

[0078] Table 1

[0079]

[0080] In summary, by introducing the structure of thioamide - benzimidazole catalyst, the present invention achieves the expected good catalytic effect, enriches the types of catalysts. At the same time, compared with the existing urea catalysts, for this catalyst, only a catalyst with a molar concentration of 0.25% relative to the monomer can quickly catalyze the ring - opening polymerization of propyl caprolactone in bulk. The synthesis is simple, the catalytic efficiency is high, the reaction conditions are relatively mild, and there is no metal residue in the product. The number - average molecular weight range of the prepared polymer can be within 1000 - 20000 g / mol, and the molecular weight distribution D ≤ 1.23. At the same time, high molecular weight and narrow molecular weight distribution of the polymer are achieved, making it have broad application prospects.

[0081] The present invention provides an idea and method for a thioamide - benzimidazole catalyst and its application in the preparation of pure bio - based block copolymers. There are many specific methods and ways to implement this technical solution. The above - mentioned is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be realized by the existing technology.

Claims

1. A method for preparing a block copolymer, characterized in that, Using lactone monomers as reaction substrates, a compound shown in Formula II and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene as catalysts, and an organic alcohol as an initiator to carry out a ring-opening polymerization reaction to prepare a block copolymer; wherein, R1 and R2 are each independently selected from hydrogen, an electron-withdrawing group, an alkyl group or an alkoxy group; wherein, the lactone monomers are a combination of lactide and propyl-caprolactone.

2. The preparation method according to claim 1, characterized in that, The block copolymer is as shown in Formula I; wherein, R1 is selected from an alkyl group having a straight-chain, branched-chain or cyclic structure of C1-C10; n≥1, m≥1; the number-average molecular weight of the block copolymer is 13,000-16,000 g / mol.

3. The preparation method according to claim 2, characterized in that, The number-average molecular weight of the segment copolymer is 13,000-15,000 g / mol, the polydispersity index is 1.18-1.23, and the glass transition temperature is -50 to -80 °C.

4. A method for preparing a homopolymer, characterized in that, Using lactone monomers as reaction substrates, a compound shown in Formula II and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene as catalysts, and an organic alcohol as an initiator to carry out a ring-opening polymerization reaction to prepare a homopolymer; wherein, R1 and R2 are each independently selected from hydrogen, an electron-withdrawing group, an alkyl group or an alkoxy group; wherein, the lactone monomer is propyl-caprolactone.

5. The preparation method according to claim 1 or 4, characterized in that In the compound shown in Formula II, the electron-withdrawing group is selected from a halogen atom, trifluoromethyl or nitro.

6. The preparation method according to claim 1 or 4, characterized in that, In the compound shown in Formula II, the electron-withdrawing group is selected from fluorine or trifluoromethyl.

7. The preparation method according to claim 1 or 4, characterized in that, In the compound shown in Formula II, the alkyl group is selected from a straight-chain alkyl group, a branched-chain alkyl group, a straight-chain alkoxy group or a branched-chain alkoxy group of C1-C10.

8. The preparation method according to claim 1 or 4, characterized in that In the compound shown in Formula II, the alkyl group is selected from a straight-chain alkyl group, a branched-chain alkyl group, a straight-chain alkoxy group or a branched-chain alkoxy group of C1-C5.

9. The preparation method according to claim 1 or 4, characterized in that, In the compound shown in Formula II, the alkyl group is selected from a straight-chain alkoxy group or a branched-chain alkoxy group of C1-C3.

10. The preparation method according to claim 1 or 4, characterized in that, In the compound shown in Formula II, the alkyl group is selected from methoxy.

11. The preparation method according to claim 1 or 4, characterized in that, The compound shown in Formula II is any one of the following Compounds II-1 to II-2; 12. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the lactone monomer to the catalyst is 1:35-65.

13. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the lactone monomer to the catalyst is 1:40-60.

14. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the lactone monomer to the catalyst is 1:45-55.

15. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the lactone monomer to the catalyst is 1:48-52.

16. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the lactone monomer to the catalyst is 1:

50.

17. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the compound shown in Formula II to 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene is 1:0.5-1.

5.

18. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the compound shown in Formula II to 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene is 1:0.7-1.

3.

19. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the compound shown in Formula II to 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene is 1:0.8-1.

2.

20. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the compound shown in Formula II to 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene is 1:0.9-1.

1.

21. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the compound shown in Formula II to 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene is 1:

1.

22. The preparation method according to claim 1 or 4, characterized in that, The organic alcohol is a straight-chain, branched-chain or cyclic organic alcohol with 1 to 10 carbon atoms.

23. The preparation method according to claim 1 or 4, characterized in that, The organic alcohol is a monohydric alcohol, dihydric alcohol, trihydric alcohol or polyhydric alcohol with 1 to 10 carbon atoms in a straight-chain, branched-chain or cyclic structure.

24. The preparation method according to claim 1 or 4, characterized in that, The organic alcohol is benzyl alcohol, butanol or p-xylene glycol.

25. The preparation method according to claim 1 or 4, characterized in that, The organic alcohol is benzyl alcohol.

26. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the lactone monomer to the organic alcohol is 50 to 115:

1.

27. The preparation method according to claim 1 or 4, characterized in that, The molar ratio of the lactone monomer to the organic alcohol is 50:

1.

28. The preparation method according to claim 1 or 4, characterized in that, The reaction is carried out without a solvent or with an organic solvent added; the organic solvent is toluene and / or tetrahydrofuran.

29. The preparation method according to claim 1 or 4, characterized in that, The reaction temperature is 20 to 100 °C.

30. The preparation method according to claim 1 or 4, characterized in that, The reaction temperature is 25 to 80 °C.

31. The preparation method according to claim 1 or 4, characterized in that, The reaction temperature is 25 to 50 °C.

32. The preparation method according to claim 1 or 4, characterized in that, After the reaction is completed, an acidic substance is added to terminate the reaction; the acidic substance is a mixed solution of benzoic acid and dichloromethane.

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