Preparation method of poly delta-thiovalerolactone

Abstract

The invention belongs to the field of polymer synthesis, and discloses a preparation method of poly (delta-thiovalerolactone), which comprises the following step: in an organic solvent, in the presence of a main catalyst and an aryl mercaptan initiator, carrying out polymerization reaction on a compound as shown in a formula (II) at 0-80 DEG C, according to the preparation method disclosed by the invention, side reactions in a polymerization process are effectively reduced, so that a monomer can be converted into poly delta-thiovalerolactone at a high conversion rate. Compared with the prior art, the high-molecular-weight poly (delta-thiovalerolactone) is obtained, and the mechanical property of the polymer can be remarkably improved due to the improvement of the molecular weight.

Description

Technical Field

[0001] The invention belongs to the field of polymer synthesis and relates to a method for preparing polydelta-thiovalerolactone. Background Art

[0002] Chemically recyclable polymers can be depolymerized into polymer precursors after use, avoiding polymer pollution and providing raw materials for polymer production. They are an effective way to improve the "white pollution" of plastics. δ-Valerolactone is a commercial reagent that can form chemically recyclable polymers through ring-opening polymerization, and the formed polyester is also biodegradable. Therefore, polyδ-valerolactone is a very valuable green polymer material. However, the melting point of this type of polymer is only 56°C, and the polymer can only be used below 56°C, and the heat resistance is poor. For this reason, improving the melting point of this type of polymer is a difficult point in research in this field. By changing the CO single bond in δ-valerolactone to a CS single bond, the melting point of the formed polyδ-thiovalerolactone can be increased to 123°C, which can be used in various fields of daily life. At the same time, the polymer main chain has a thioester functional group, which ensures the degradability of the polymer. However, the currently disclosed methods can only obtain polyδ-thiovalerolactone with a number average molecular weight of less than 14.3kg / mol. δ-thiovalerolactone ring-opening polymerization is an effective method for preparing polyδ-thiovalerolactone. Currently, there are two papers reporting the preparation of polyδ-thiovalerolactone by ring-opening polymerization of δ-thiovalerolactone. The Overberger group (J.Am.Chem.Soc.1968,90,3533) used anionic polymerization to obtain polyδ-thiovalerolactone with low molecular weight (number average molecular weight M n ~1.0kg / mol), the molecular weight of polyδ-thiovalerolactone obtained by Gutekunst using organic base and alkyl mercaptan is also very low (number average molecular weight M n ~14.3kg / mol)(ACSMacro Lett.2022,11,895), poor mechanical properties and no application value.

[0003] Therefore, the development of an effective catalytic system for the polymerization of δ-thiovalerolactone to prepare high molecular weight polyδ-thiovalerolactone is still a technical gap. Polymer chemistry points out that the molecular weight of a polymer will only show good mechanical properties after reaching the critical entanglement molecular weight. The entanglement molecular weight can be calculated by the Likhtman-Mcleish theory in polymer physics. For this reason, we determined the entanglement molecular weight of the polymer through oscillatory shear rheology experiments. We measured the dynamic storage modulus (G'), loss modulus (G") and complex viscosity (η *) and the rheometer frequency were measured, and the Williams-Randall-Ferry theory was used, and the data analysis software TRIOS (TA Instruments, USA) was used to automatically fit the time-temperature-amplitude superposition at 127°C to obtain Figure 1 Using the McIlroy model (https: / / www.stevenabbott.co.uk / practical-rheology / L-M_Mc.php), Figure 1 The data import in can be deduced that the entanglement molecular weight of polyδ-thiovalerolactone is 16kg / mol. That is to say, when the molecular weight of polyδ-thiovalerolactone reaches above 16kg / mol, the polymer shows obvious chain entanglement, thereby obtaining polyδ-thiovalerolactone with practical mechanical properties. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the low molecular weight of the existing polyδ-thiovalerolactone (PTVL), and provide a preparation method of polyδ-thiovalerolactone. The number average molecular weight of the polyδ-thiovalerolactone prepared by the preparation method of the present invention is significantly improved.

[0005] The technical solution of the present invention:

[0006] A method for preparing polyδ-thiovalerolactone comprises the following steps: in an organic solvent, in the presence of a main catalyst and an aromatic mercaptan initiator, polymerizing a compound represented by formula (II) at 0 to 80°C;

[0007]

[0008] The main catalyst is one or a mixture of two or more of amidine organic bases, guanidine organic bases, N-heterocyclic carbene organic bases, and N-heterocyclic olefin organic bases, preferably amidine organic bases.

[0009] In the method for preparing the compound as shown in formula (I), the organic solvent is a conventional organic solvent in the art, preferably a mixture of one or more of halogenated hydrocarbon solvents, cyclic ether solvents, aromatic hydrocarbon solvents, and halogenated aromatic hydrocarbon solvents, more preferably aromatic hydrocarbon solvents and / or halogenated aromatic hydrocarbon solvents, more preferably toluene and / or o-dichlorobenzene. The halogenated hydrocarbon solvent is preferably a mixture of one or more of dichloromethane, chloroform, 1,2-dichloroethane and tetrachloroethane. The cyclic ether solvent is preferably tetrahydrofuran and / or dioxane. The aromatic hydrocarbon solvent is preferably a mixture of one or more of toluene, benzene and xylene, more preferably toluene. The halogenated aromatic hydrocarbon solvent is preferably a mixture of one or more of o-dichlorobenzene, o-difluorobenzene, o-dibromobenzene, chlorobenzene, fluorobenzene, bromobenzene and iso-trichlorobenzene, more preferably o-dichlorobenzene.

[0010] The amidine organic base is a conventional amidine organic base in the art, preferably 1,8-diazabicyclo[5.4.0]undec-7-ene (Formula III), the structure of which is shown below:

[0011]

[0012] The guanidine organic base may be a conventional guanidine organic base in the art, preferably 1,5,7-triazidebicyclo(4.4.0)dec-5-ene (IV) and / or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (V), the structure of which is shown below:

[0013]

[0014] The carbene organic base is a compound as shown in formula (VI), and its structure is shown below:

[0015]

[0016] Among them, R 1 and R 2 R is independently hydrogen, a hydrocarbon group of 1 to 20 carbon atoms or an aromatic group of 6 to 20 carbon atoms, which may be the same or different; 3 and R 4 They are independently a hydrocarbon group of 1 to 20 carbon atoms or an aryl group of 6 to 20 carbon atoms, which may be the same or different.

[0017] The N-heterocyclic carbene organic base is a compound represented by formula (VII), and its structure is shown below:

[0018]

[0019] Among them, R 6 and R 7 R is independently hydrogen, a hydrocarbon group of 1 to 20 carbon atoms or an aromatic group of 6 to 20 carbon atoms, which may be the same or different; 5 and R 8 R is independently a hydrocarbon group of 1 to 20 carbon atoms or an aryl group of 6 to 30 carbon atoms; 9 and R 10 are independently hydrogen, methyl or ethyl.

[0020] The aromatic thiol initiator is R 15 CH2SH、SCH2R 16 CH2SH、R 17 (CH2SH)3、R 18 (CH2SH)4 or a mixture of two or more, R 15 , R 16 , R17 and R 18 It is an aromatic group having 6 to 20 carbon atoms, and the four are the same or different.

[0021] The molar ratio of the compound represented by formula (II) to the main catalyst is 100:1-10000:1; the molar ratio of the aromatic thiol initiator to the catalyst is 1:1-100:1.

[0022] The polymerization reaction time is 5-1440 minutes.

[0023] The present invention realizes the preparation of a high molecular weight polymer represented by formula (I) using a compound represented by formula (II) through the following strategy: using a weakly nucleophilic aromatic thiol reagent as an initiator. The nucleophilicity of the reagent is significantly lower than that of alkyl thiols reported in the literature, so that a more stable thiolactone initiating end is formed after initiation of polymerization, and the chain end is not easy to perform nucleophilic attack on the initiating end, thereby avoiding chain termination, facilitating the polymerization reaction, and obtaining a high molecular weight polymer.

[0024]

[0025] Without violating the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0026] The reagents and raw materials used in the present invention are commercially available.

[0027] Beneficial effects of the invention: The preparation method of the invention effectively reduces the side reactions in the polymerization process, so that the monomer can be converted into polyδ-thiovalerolactone at a high conversion rate. Compared with the method reported in the literature, a high molecular weight polyδ-thiovalerolactone that cannot be synthesized in the literature is obtained, and the increase in molecular weight can significantly improve the mechanical properties of the polymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the NMR of the polymerized monomer (II) δ-thiovalerolactone.

[0029] Figure 2 This is the rheological test result of polyδ-thiovalerolactone. The entanglement molecular weight of the polymer is 16kg / mol. The polymer molecular weight exceeds 16kg / mol to show good mechanical properties. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0031] Example 1

[0032] The compound represented by formula (II) of the present invention is a homemade product, and its initial raw material is commercial δ-valerolactone, which is prepared by a one-step reaction. The preparation method is not particularly limited, and is preferably prepared according to the method described in the following document (ACS MacroLett.2022,11,895-901):

[0033] In a 500mL three-necked bottle, 20.0g of 4-vinylpentanoic acid and 5.13g of benzoin dimethyl ether were added, 50mL of ethyl acetate was added and stirred, and then 30.4g of thioacetic acid was added thereto, and 365nm ultraviolet light was irradiated for 4 hours. The solvent was removed by vacuum distillation (100°C, 0.12mmHg) to obtain 26.0g of the intermediate.

[0034] The intermediate obtained above was placed in a 2000 ml flask, and 1400 ml of 1 mol / L NaOH methanol / water solution (volume ratio 9 / 1) was added, and heated at 90°C for 4 hours. Then, the mixture was extracted with dichloromethane 5 times, and the solvent was removed from the obtained mixture to obtain 5-mercapto-pentanoic acid. 12 L of dichloromethane, 48 mL of N, N-diisopropylethylamine, and 64 g of 2-(7-azabenzotriazole)-N, N, N', N'-tetramethyluronium hexafluorophosphate were added, and stirred at room temperature for 12 hours. The solvent was removed, and column chromatography was performed (ether / hexane = 10:1) to obtain 10.2 g of δ-thiovalerolactone.

[0035] The present invention characterizes the obtained δ-thiovalerolactone monomer by nuclear magnetic resonance (NMR). 1 H NMR spectrum Figure 1 As shown, it is consistent with the literature report, which proves that the δ-thiocarbonyl valerolactone monomer prepared by the present invention has the structure of formula (II).

[0036]

[0037] Example 2

[0038] At 20°C, in a pre-dried 10 mL serum bottle, first weigh 2.0 g (8.61 mmol) of δ-thiovalerolactone monomer, and weigh 4.27 mg (0.0344 mmol) of benzyl mercaptan and 5.24 mg (0.0344 mmol) of catalyst DBU and dissolve them in 0.07 mL of toluene. Mix well and add to the δ-thiovalerolactone monomer. After a while, add 5 mL of trifluoroacetic acid / CDCl3 (10 mg / mL) to immediately quench the polymerization reaction, and then use 1H NMR was used to analyze the monomer conversion. The quenched mixture was then precipitated into cold methanol, filtered, washed three times with cold methanol to remove any unreacted monomer, and dried overnight in a vacuum oven at room temperature to a constant weight. 1.62 g of a light yellow solid was obtained. The average molecular weight of the polymer was 17.3 kg / mol and the molecular weight distribution was 2.03 as determined by gel chromatography. The melting point of the polymer was 123 °C as shown by DSC testing.

[0039] Example 3

[0040] At 20°C, in a pre-dried 10mL serum bottle, first weigh 1.0g (8.61mmol) of the monomer δ-thiovalerolactone, and weigh 2.13mg (0.0172mmol) of the initiator benzyl mercaptan and 2.62mg (0.0172mmol) of the catalyst DBU and dissolve them in 0.07mL of toluene. Mix well and add to the monomer δ-thiovalerolactone. After a while, add 5mL of benzoic acid / CDCl3 (10mg / mL) to immediately quench the polymerization reaction, and then use 1 H-NMR was used to analyze the conversion of the monomers. The quenched mixture was then precipitated into cold methanol, filtered, washed three times with cold methanol to remove any unreacted monomers, and dried overnight in a vacuum oven at room temperature to a constant weight. 0.91 g of a light yellow solid was obtained. The average molecular weight of the polymer was 18.2 kg / mol and the molecular weight distribution was 1.81 as determined by gel chromatography. The melting point of the polymer was 123°C as shown by DSC testing.

[0041] Example 4

[0042] At 20°C, in a pre-dried 10mL serum bottle, first weigh 1.0g (8.61mmol) of the monomer δ-thiovalerolactone, and weigh 1.06mg (0.00861mmol) of the initiator benzyl mercaptan and 1.31mg (0.00861mmol) of the catalyst DBU and dissolve them in 0.07mL of toluene. Mix well and add to the monomer δ-thiovalerolactone. After a while, add 5mL of benzoic acid / CDCl3 (10mg / mL) to immediately quench the polymerization reaction, and then use 1 H NMR was used to analyze the monomer conversion. The quenched mixture was then precipitated into cold methanol, filtered, washed three times with cold methanol to remove any unreacted monomer, and dried overnight in a vacuum oven at room temperature to a constant weight. 0.82 g of a light yellow solid was obtained. The average molecular weight of the polymer was determined by gel chromatography to be 23.1 kg / mol, the molecular weight distribution was 1.68, and the DSC test showed that the melting point of the polymer was 123°C.

[0043] Example 5

[0044] At 20°C, in a pre-dried 10mL serum bottle, first weigh 1.0g (17.2mmol) of the monomer δ-thiovalerolactone, and weigh 0.53mg (0.0043mmol) of the initiator benzyl mercaptan and 2.62mg (0.0172mmol) of the catalyst DBU and dissolve them in 0.07mL of toluene. Mix well and add to the monomer δ-thiovalerolactone. After a while, add 5mL of benzoic acid / CDCl3 (10mg / mL) to immediately quench the polymerization reaction, and then use 1 H NMR was used to analyze the monomer conversion. The quenched mixture was then precipitated into cold methanol, filtered, washed three times with cold methanol to remove any unreacted monomer, and dried overnight in a vacuum oven at room temperature to a constant weight. 1.50 g of a light yellow solid was obtained. The average molecular weight of the polymer was 54.4 kg / mol and the molecular weight distribution was 2.35 as determined by gel chromatography. The melting point of the polymer was 123 °C as shown by DSC testing.

[0045] Example 6

[0046] At 20°C, in a pre-dried 10mL serum bottle, first weigh 2g (17.2mmol) of monomer thiovalerolactone, and weigh 0.53mg (0.0043mmol) of initiator benzyl mercaptan and 3.27mg (0.043mmol) of catalyst DBU and dissolve them in 0.07mL of toluene. Mix well and add to the monomer δ-thiovalerolactone. After a while, add 5mL of benzoic acid / CDCl3 (10mg / mL) to immediately quench the polymerization reaction, and then use 1 H NMR was used to analyze the monomer conversion. The quenched mixture was then precipitated into cold methanol, filtered, washed three times with cold methanol to remove any unreacted monomer, and dried overnight in a vacuum oven at room temperature to a constant weight. 1.30 g of a light yellow solid was obtained. The average molecular weight of the polymer was determined by gel chromatography to be 92.1 kg / mol, the molecular weight distribution was 2.35, and the DSC test showed that the melting point of the polymer was 123°C.

[0047] Example 7

[0048] 1.0 g of polyδ-thiovalerolactone obtained in Example 7 and 10 mg of phosphomolybdic acid were added to a round-bottom flask, and the vacuum degree was 0.07 torr and the temperature was 160° C. to obtain 0.97 g of δ-thiovalerolactone. The purity was greater than 99% as determined by nuclear magnetic resonance.

[0049] Comparative Example 1

[0050] This comparative example is a reported method of polymerizing δ-thiovalerolactone using DBU and alkylthiols, literature: Stellmach K.A.; Paul MKK; Xu M.; Su YL; Fu L.; Toland AR; Tran H.; Chen L.; Ramprasad R.; Gutekunst WRACS Macro Lett, 2022, 11, 895–901.

[0051] The polymerization of δ-thiovalerolactone was repeated according to the conditions in the literature (catalyst: DBU, molar ratio of DBU to δ-thiovalerolactone: 200:1, tetrahydrofuran as solvent, monomer concentration: 5 mol / L, polymerization temperature: 20°C, reaction time: 0.5 h). The polymerization results were consistent with those in the literature (monomer conversion: 46%, M n =14.3kg / mol, melting point 123°C) similar: M n =14.4 kg / mol, monomer conversion =45%, melting point 123°C).

[0052] Comparative Example 2

[0053] This comparative example is based on comparative example 1, but the molar ratio of δ-thiovalerolactone to DBU is further increased to 1000:1 (the catalyst is DBU, the molar ratio of DBU to benzyl mercaptan is 1:1, tetrahydrofuran is used as the solvent, the monomer concentration is 5 mol / L, the polymerization temperature is 20°C, and the reaction time is 0.5 hour), while other conditions remain unchanged. The molecular weight of the polymer obtained by polymerization is almost unchanged and is still 14.0 kg / mol, but the monomer conversion rate is reduced to 30%.

[0054] Compared with the polymerization conditions of Example 4 of the present invention and Comparative Example 2, except for the different initiators (Example 2 uses aryl mercaptan, and the comparative example uses alkyl mercaptan), the other conditions are exactly the same. Example 2 obtains a polyδ-thiocarbonyl valerolactone with a molecular weight of 23.1 kg / mol, while the comparative example only obtains a polymer with a molecular weight of 14.0 kg / mol. Therefore, the aryl mercaptan initiator in the present invention is an important factor in producing high molecular weight polyδ-thiocarbonyl valerolactone.

Claims

1. A method for preparing polyδ-thiovalerolactone, characterized in that: The method comprises the following steps: in an organic solvent, in the presence of a main catalyst and an aromatic mercaptan initiator, polymerizing a compound represented by formula (II) at 0 to 80° C. to generate polyδ-thiovalerolactone represented by formula (I); 2. The preparation method according to claim 1, characterized in that: The main catalyst is one or a mixture of two or more of an amidine organic base, a guanidine organic base, an N-heterocyclic carbene organic base, and an N-heterocyclic olefin organic base; The organic solvent is one or a mixture of two or more of a halogenated hydrocarbon solvent, a cyclic ether solvent, an aromatic hydrocarbon solvent, or a halogenated aromatic hydrocarbon solvent; The aromatic thiol initiator is R 15 CH2SH、SCH2R 16 CH2SH、R 17 (CH2SH)3、R 18 (CH2SH)4 or a mixture of two or more, R 15 , R 16 , R 17 and R 18 is an aromatic group of 6 to 20 carbon atoms, the four being the same or different; The molar ratio of the compound represented by formula (II) to the main catalyst is 100:1-10000:1; the molar ratio of the aromatic thiol initiator to the main catalyst is 1:1-100:1; The polymerization reaction time is 5-1440 minutes.

3. The preparation method according to claim 2, characterized in that: The amidine organic base is 1,8-diazabicyclo[5.4.0]undec-7-ene (Formula III), and its structure is shown below:

4. The preparation method according to claim 2, characterized in that: The guanidine organic base is a 1,5,7-triazidebicyclo(4.4.0)dec-5-ene of formula (IV) and / or a 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene of formula (V), and the structures of the two are shown below:

5. The preparation method according to claim 2, characterized in that: The carbene organic base is a compound as shown in formula (VI), and its structure is shown below: Among them, R 1 and R 2 R is independently hydrogen, a hydrocarbon group of 1 to 20 carbon atoms or an aryl group of 6 to 20 carbon atoms, which may be the same or different; 3 and R 4 They are independently a hydrocarbon group of 1 to 20 carbon atoms or an aryl group of 6 to 20 carbon atoms, which may be the same or different.

6. The preparation method according to claim 2, characterized in that: The N-heterocyclic carbene organic base is a compound represented by formula (VII), and its structure is shown below: Among them, R 6 and R 7 R is independently hydrogen, a hydrocarbon group of 1 to 20 carbon atoms or an aryl group of 6 to 20 carbon atoms, which may be the same or different; 5 and R 8 R is independently a hydrocarbon group of 1 to 20 carbon atoms or an aryl group of 6 to 30 carbon atoms; 9 and R 10 are independently hydrogen, methyl or ethyl.

7. The preparation method according to claim 2, characterized in that: The organic solvent is an aromatic hydrocarbon solvent and / or a halogenated aromatic hydrocarbon solvent.

8. The preparation method according to claim 2, characterized in that: The aromatic hydrocarbon solvent is one or a mixture of two or more of toluene, benzene and xylene; The halogenated aromatic hydrocarbon solvent is one or a mixture of two or more of o-dichlorobenzene, o-difluorobenzene, o-dibromobenzene, chlorobenzene, fluorobenzene, bromobenzene and s-trichlorobenzene; The halogenated hydrocarbon solvent is one or a mixture of two or more of dichloromethane, trichloromethane, 1,2-dichloroethane and tetrachloroethane; The cyclic ether solvent is tetrahydrofuran and / or dioxane.

Images