A method for preparing polyδ-thiovalactone

Abstract

This invention belongs to the field of polymer synthesis and discloses a method for preparing polyδ-thiovalerate, which includes the following steps: in an organic solvent, in the presence of a main catalyst and an aryl thiol initiator, the compound shown in formula (II) is polymerized at 0-80°C. The preparation method of this invention effectively reduces side reactions during polymerization, allowing the monomer to be converted into polyδ-thiovalerate with a high conversion rate. Compared with existing technologies, high molecular weight polyδ-thiovalerate is obtained, and the increase in molecular weight significantly improves the mechanical properties of the polymer.

Description

Technical Field

[0001] This invention belongs to the field of polymer synthesis and relates to a method for preparing polyδ-thiovalerate. Background Technology

[0002] Chemically recyclable polymers can depolymerize into polymer precursors after use, avoiding polymer pollution and providing raw materials for polymer production, making them an effective method to improve the "white pollution" caused by plastics. δ-valerolactone is a commercially available reagent that can form chemically recyclable polymers through ring-opening polymerization, and the resulting polyesters are also biodegradable. Therefore, polyδ-valerolactone is a very valuable green polymer material. However, the melting point of this type of polymer is only 56℃, limiting its use to below 56℃ and indicating poor heat resistance. Therefore, increasing the melting point of this type of polymer is a research challenge in this field. By changing the CO single bond in δ-valerolactone to a CS single bond, the melting point of the resulting polyδ-thiovalerolactone can be increased to 123℃, making it suitable for various applications in daily life. Simultaneously, the polymer backbone has thioester functional groups, ensuring the polymer's biodegradability. However, currently available methods can only yield polyδ-thiovalerolactone with a number-average molecular weight of less than 14.3 kg / mol. Ring-opening polymerization of δ-thiovalactone is an effective method for preparing polyδ-thiovalactone. Two papers have reported the preparation of polyδ-thiovalactone by ring-opening polymerization of δ-thiovalactone. Overberger's group (J. Am. Chem. Soc. 1968, 90, 3533) obtained polyδ-thiovalactone with low molecular weight (number average molecular weight M) through anionic polymerization. n ~1.0 kg / mol), Gutekunst obtained polyδ-thiovalerate using organic bases and alkyl thiols, which also has a very low molecular weight (number average molecular weight M). n ~14.3 kg / mol) (ACS Macro Lett. 2022, 11, 895), with poor mechanical properties and no application value.

[0003] Therefore, developing an effective catalytic system for the polymerization of δ-thiovalactone to prepare high molecular weight polyδ-thiovalactone remains a technological gap. Polymer chemistry indicates that good mechanical properties are only observed after the polymer reaches the critical entanglement molecular weight. The entanglement molecular weight can be calculated using the Likhtman-Mcleish theory in polymer physics. Therefore, we determined the entanglement molecular weight of this polymer through oscillatory shear rheological experiments. We analyzed the dynamic storage modulus (G'), loss modulus (G''), and composite viscosity (η) of polyδ-thiovalactone at different temperatures. *The relationship between the frequency of the instrument and the frequency of the rheometer was determined using the Williams-Randall-Ferry theory and automatic fitting by the data analysis software TRIOS (TA Instruments, Inc., USA). Time-temperature-amplitude superposition was performed at 127℃ to obtain the desired results. Figure 2 Using the model publicly available by McIlroy (https: / / www.stevenabbott.co.uk / practical-rheology / L-M_Mc.php), we can... Figure 2 The imported data shows that the entangled molecular weight of polyδ-thiovalactone is 16 kg / mol. In other words, when the molecular weight of polyδ-thiovalactone reaches 16 kg / mol or higher, the polymer exhibits obvious chain entanglement, thus obtaining polyδ-thiovalactone with practical mechanical properties. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the low molecular weight of existing poly(δ-thiovalactone) (PTVL) and to provide a method for preparing poly(δ-thiovalactone). The number-average molecular weight of poly(δ-thiovalactone) prepared by the method of this invention is significantly improved.

[0005] The technical solution of this invention:

[0006] A method for preparing polyδ-thiovalerate includes the following steps: in an organic solvent, in the presence of a main catalyst and an aryl thiol initiator, the compound shown in formula (II) is polymerized at 0~80℃.

[0007] , .

[0008] The main catalyst is one or a mixture of two or more of the following: amidine organic bases, guanidine organic bases, N-heterocyclic carbene organic bases, and N-heterocyclic olefin organic bases, with amidine organic bases being preferred.

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

[0010] The amidine organic bases mentioned are conventional amidine organic bases 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 bases described herein may be conventional guanidine organic bases in the art, preferably 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (IV) and / or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (V), the structures of which are shown below:

[0013] , .

[0014] The carbene organic bases mentioned above are compounds of formula (VI), with the following structures:

[0015] ;

[0016] Among them, R 1 and R 2 Independently composed of hydrogen, a hydrocarbon group with 1 to 20 carbon atoms, or an aryl group with 6 to 20 carbon atoms, which may be the same or different; R 3 and R 4 It can be a hydrocarbon group with 1 to 20 carbon atoms or an aryl group with 6 to 20 carbon atoms, which may be the same or different.

[0017] The N-heterocyclic carbene organic bases described herein are compounds of formula (VII), and their structures are shown below:

[0018] ;

[0019] Among them, R 6 and R7 Independently composed of hydrogen, a hydrocarbon group with 1 to 20 carbon atoms, or an aryl group with 6 to 20 carbon atoms, which may be the same or different; R 5 and R 8 Independently a hydrocarbon group of 1–20 carbon atoms or an aryl group of 6–30 carbon atoms; R 9 and R 10 It can be hydrogen, methyl, or ethyl on its own.

[0020] The aryl thiol initiator is R 15 CH2SH, HSCH2R 16 CH2SH, R 17 (CH2SH)3、R 18 One or more of (CH2SH)4, R 15 、R 16 、R 17 and R 18 It consists of aryl groups with 6 to 20 carbon atoms, and the four groups may be the same or different.

[0021] The molar ratio of the compound as shown in formula (II) to the main catalyst is 100:1 to 10000:1; the molar ratio of the aryl thiol initiator to the catalyst is 1:1 to 100:1.

[0022] The polymerization reaction takes 5-1440 minutes.

[0023] This invention achieves the preparation of high molecular weight polymers of formula (I) using compounds of formula (II) through the following strategy: using a weakly nucleophilic aryl thiol reagent as an initiator. The nucleophilicity of this reagent is significantly lower than that of alkyl thiols reported in the literature. This results in the formation of a more stable thiolactone initiating end after polymerization, making it less likely for the chain end to nucleophilically attack the initiating end, thus avoiding chain termination and facilitating the polymerization reaction to obtain a high molecular weight polymer.

[0024]

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

[0026] The reagents and raw materials used in this invention are all commercially available.

[0027] The beneficial effects of this invention are as follows: The preparation method of this invention effectively reduces side reactions during the polymerization process, enabling the monomer to be converted into polyδ-thiovalerate with a high conversion rate. Compared with the methods reported in the literature, high molecular weight polyδ-thiovalerate that cannot be synthesized in the literature is obtained, and the increase in molecular weight can significantly improve the mechanical properties of the polymer. Attached Figure Description

[0028] Figure 1 It is the NMR of the polymeric monomer (II) δ-thiovalactone.

[0029] Figure 2 The results are from the rheological tests of poly(δ-thiovalerate). The entanglement molecular weight of the polymer is 16 kg / mol. Only polymers with a molecular weight exceeding 16 kg / mol can exhibit good mechanical properties. Detailed Implementation

[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 of formula (II) described in this invention is a self-made product, prepared from commercially available δ-valerolactone via a one-step reaction. There are no particular limitations on the preparation method, but it is preferably prepared according to the method described in the following literature (ACS Macro Lett. 2022, 11, 895−901):

[0033] 20.0 g of 4-vinylpentanoic acid and 5.13 g of benzoin dimethyl ether were added to a 500 mL three-necked flask, followed by stirring with 50 mL of ethyl acetate. Then, 30.4 g of thioacetic acid was added, and the mixture was irradiated with 365 nm ultraviolet light for 4 hours. The solvent was removed under vacuum, and the mixture was distilled under reduced pressure (100 °C, 0.12 mmHg) to obtain 26.0 g of the intermediate.

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

[0035] The δ-thiovalactone monomer obtained in this invention was characterized by nuclear magnetic resonance (NMR). 1 H NMR spectrum as follows Figure 1 As shown, this is consistent with literature reports. This demonstrates that the δ-thiocarbonylpentanolide monomer prepared in this 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 monomer δ-thiovalactone, and separately weigh 4.27 mg (0.0344 mmol) of benzyl mercaptan and 5.24 mg (0.0344 mmol) of catalyst DBU, dissolve them in 0.07 mL of toluene, mix thoroughly, and then add to the monomer δ-thiovalactone. After a period of time, add 5 mL of trifluoroacetic acid / CDCl3 (10 mg / mL) to immediately quench the polymerization reaction, and then use... 1 The monomer conversion was determined by ¹H NMR analysis. The quenched mixture was then precipitated in cold methanol, filtered, washed three times with cold methanol to remove any unreacted monomers, and dried overnight at room temperature in a vacuum oven to constant weight. 1.62 g of a pale yellow solid was obtained. Gel chromatography determined the average molecular weight of the polymer to be 17.3 kg / mol with a molecular weight distribution of 2.03. DSC analysis showed the polymer melting point to be 123 °C.

[0039] Example 3

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

[0041] Example 4

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

[0043] Example 5

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

[0045] Example 6

[0046] At 20 °C, in a pre-dried 10 mL serum bottle, 2 g (17.2 mmol) of thiovalactone monomer was weighed first. Separately, 0.53 mg (0.0043 mmol) of initiator benzyl mercaptan and 3.27 mg (0.043 mmol) of catalyst DBU were dissolved in 0.07 mL of toluene, mixed thoroughly, and then added to the δ-thiovalactone monomer. After a period of time, 5 mL of benzoic acid / CDCl3 (10 mg / mL) was added to immediately quench the polymerization reaction, and then... 1 The monomer conversion was determined by ¹H NMR analysis. The quenched mixture was then precipitated in cold methanol, filtered, washed three times with cold methanol to remove any unreacted monomers, and dried overnight at room temperature in a vacuum oven to constant weight. 1.30 g of a pale yellow solid was obtained. Gel chromatography determined the average molecular weight of the polymer to be 92.1 kg / mol with a molecular weight distribution of 2.35. DSC analysis showed the polymer melting point to be 123 °C.

[0047] Example 7

[0048] 1.0 g of poly(δ-thiovalactone) obtained in Example 1 was added to a round-bottom flask, along with 10 mg of phosphomolybdic acid. The mixture was heated under vacuum of 0.07 torr at 160°C to obtain 0.97 g of δ-thiovalactone. NMR spectroscopy determined the purity to be greater than 99%.

[0049] Comparative Example 1

[0050] This comparative example is a previously reported polymerization of δ-thiovalerate using DBU and alkyl thiols, reference: Stellmach K. A.; Paul MKK; Xu M.; Su YL; Fu L.; Toland AR; Tran H.; Chen L.; Ramprasad R.; Gutekunst WR ACS Macro Lett, 2022, 11, 895–901.

[0051] The polymerization of δ-thiovalactone was repeated under the conditions described in the literature (catalyst: DBU, molar ratio of DBU to δ-thiovalactone: 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%). n =14.3 kg / mol, melting point 123℃) similar to: M n =14.4 kg / mol, monomer conversion =45%, melting point 123℃).

[0052] Comparative Example 2

[0053] This comparative example is based on Comparative Example 1, with the molar ratio of δ-thiovalactone to DBU increased to 1000:1 (catalyst is DBU, the molar ratio of DBU to alkyl thiols is 1:1, tetrahydrofuran is used as solvent, monomer concentration is 5 mol / L, polymerization temperature is 20℃, and reaction time is 0.5 hours). With other conditions unchanged, the molecular weight of the polymer obtained by polymerization is almost unchanged, still 14.0 kg / mol, but the monomer conversion rate is reduced to 30%.

[0054] Compared with Comparative Example 2, Example 4 of this invention uses the same polymerization conditions except for the initiator (Arylthiol was used in Example 2, while alkylthiol was used in the comparative example). Example 2 yielded poly(δ-thiocarbonylpentanolide) with a molecular weight of 23.1 kg / mol, while the comparative example only yielded a polymer with a molecular weight of 14.0 kg / mol. Therefore, the arylthiol initiator in this invention is an important factor in the production of high molecular weight poly(δ-thiocarbonylpentanolide).

Claims

1. A method for preparing polyδ-thiovalactone, characterized in that, The process includes the following steps: In an organic solvent, in the presence of a main catalyst and an aryl thiol initiator, the compound shown in formula (II) is polymerized at 0~80°C to generate poly(δ-thiopentalol) formula (I); 、 ； The main catalyst is one or a mixture of two or more of the following: amidine organic bases, guanidine organic bases, N-heterocyclic carbene organic bases, and N-heterocyclic olefin organic bases; The aryl thiol initiator is R 15 CH2SH, HSCH2R 16 CH2SH, R 17 (CH2SH)3、R 18 One or more of (CH2SH)4, R 15 R 16 R 17 and R 18 It consists of aryl groups with 6 to 20 carbon atoms, and the four groups may be the same or different.

2. The preparation method according to claim 1, characterized in that, The organic solvent is one or a mixture of two or more of the following: halogenated hydrocarbon solvents, cyclic ether solvents, aromatic hydrocarbon solvents, and halogenated aromatic hydrocarbon solvents; The molar ratio of the compound shown in formula (II) to the main catalyst is 100:1 to 10000:1; the molar ratio of the aryl thiol initiator to the main catalyst is 1:1 to 100:1; The polymerization reaction takes 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, and its structure is shown below: 。 4. The preparation method according to claim 2, characterized in that, The guanidine organic bases mentioned are of formula (IV) 1,5,7-triazidobicyclo(4.4.0)dec-5-ene and / or formula (V) 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, the structures of which are shown below: 、 。 5. The preparation method according to claim 2, characterized in that, The carbene organic bases mentioned are compounds of formula (VI), with the following structures: ； Among them, R 1 and R 2 Independently composed of hydrogen, a hydrocarbon group with 1 to 20 carbon atoms, or an aryl group with 6 to 20 carbon atoms, which may be the same or different; R 3 and R 4 It can be a hydrocarbon group with 1 to 20 carbon atoms or an aryl group with 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 ene organic bases are compounds as shown in formula (VII), and their structures are as follows: ； Among them, R 6 and R 7 Independently composed of hydrogen, a hydrocarbon group with 1 to 20 carbon atoms, or an aryl group with 6 to 20 carbon atoms, which may be the same or different; R 5 and R 8 Independently a hydrocarbon group of 1–20 carbon atoms or an aryl group of 6–30 carbon atoms; R 9 and R 10 It can be hydrogen, methyl, or ethyl on its own.

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

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

Images