Sulfur-containing polymer based on polyethylene skeleton as well as preparation method and application of sulfur-containing polymer

Abstract

The invention provides a sulfur-containing polymer based on a polyethylene skeleton as well as a preparation method and application of the sulfur-containing polymer. According to the invention, dihalogenated hydrocarbon and alkali metal sulfide are subjected to a continuous nucleophilic substitution reaction in a toluene solvent under an inert atmosphere condition to obtain a sulfur-containing polymer with a polyethylene skeleton, and sulfur atoms are introduced into a main chain of a polyethylene long chain. According to the preparation method, in the synthesis process, reactants are simple and cheap, the product is obtained through a one-pot method, loss caused by multi-step reaction is reduced, and the yield is high.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a sulfur-containing polymer based on a polyethylene backbone, its preparation method, and its application. Background Technology

[0002] Ground mulching film agriculture technology emerged as a new cultivation technique in my country during the 1970s. This technology involves applying a 0.01-0.02mm thick transparent or colored plastic film tightly to the ground surface for cultivation. It is the simplest and most convenient form of protected cultivation. Its functions include increasing soil temperature, promoting root development, and thus increasing crop yield and value. In addition, mulching film also effectively conserves moisture, saves water, controls weeds, promotes the decomposition of organic fertilizers, and keeps the soil loose (preventing soil compaction).

[0003] Traditional plastic film used for mulching is characterized by high strength, light weight, corrosion resistance, ease of processing, and low price, making it widely used in people's production and daily life. However, while bringing great convenience, it also brings serious negative impacts. Because discarded plastic film is covered in clay and cannot be recycled, its presence in farmland affects soil quality and crop cultivation, taking approximately a century to degrade. Long-term residue in the natural environment can cause serious environmental pollution, affecting not only the ecological balance but also threatening human health. If the used plastic film cannot degrade, its residue in the soil will cause white pollution.

[0004] Although a number of new biodegradable films have emerged, such as the common ones: 1) starch-based biodegradable films, they dissolve quickly in humid environments, have unstable degradation rates, poor mechanical properties, and low heat resistance; 2) polylactic acid (PLA) films, which are not only expensive to produce, but also have degradation rates that are greatly affected by environmental conditions, and their degradation products can have a certain impact on soil and the environment; 3) cellulose-based biodegradable films also have a slow degradation rate; 4) polyhydroxyalkanoate (PHA) films cannot be mass-produced at present, have high costs, and their degradation rates are also greatly affected by the environment; 5) plant residues or straw can also be used as mulch, but this can easily lead to weed growth or pests, affecting crop growth.

[0005] Introducing sulfur into the backbone of carbon-chain polymers yields sulfur-containing polymers based on a polyethylene backbone, which possess both high mechanical strength and excellent biodegradability, particularly in soil and within organisms. However, the current preparation process for these sulfur-containing polymers is complex, resulting in low yields and increased production costs.

[0006] Therefore, there is an urgent need to provide a biodegradable material that is simple to produce, low in cost, and has good degradation properties. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a sulfur-containing polymer based on a polyethylene backbone.

[0008] Another object of the present invention is to provide a method for preparing the sulfur-containing polymer based on the polyethylene backbone.

[0009] Another object of the present invention is to provide the application of the sulfur-containing polymer based on the polyethylene skeleton in the preparation of mulch films.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a sulfur-containing polymer based on a polyethylene backbone, comprising the following steps: The dihalogenated hydrocarbon and alkali metal sulfide are dissolved in toluene to obtain a reaction solution. Then, a continuous nucleophilic substitution reaction is carried out at 120-140°C for 48-96 hours in an inert atmosphere. After purification, the sulfur-containing polymer based on the polyethylene backbone is obtained.

[0011] This invention uses dihalogenated hydrocarbons and alkali metal sulfides as reactants, and carries out a continuous nucleophilic substitution reaction in toluene solvent at a relatively high temperature. The alkali metal sulfides themselves act as excellent nucleophiles, continuously substituting halogen substituents to complete carbon chain growth, resulting in a sulfur-containing polymer with a polyethylene backbone, and introducing sulfur atoms into the long polyethylene backbone. The preparation method of this invention uses simple reactants (containing only reactants and solvent), is low-cost, and obtains the product in a one-pot process, reducing losses caused by multiple reaction steps and achieving high yield.

[0012] In this polymer, the polyethylene backbone has excellent mechanical properties and thermal stability. The introduction of sulfur atoms into the polyethylene backbone can form biologically attackable chemical bonds that facilitate degradation, achieving a slow degradation effect. The introduction of sulfur atoms into agriculture can also alleviate the problem of sulfur deficiency in soil and help plant growth.

[0013] Toluene has low toxicity, a high boiling point, and high solubility for the reactants. Since nucleophilic substitution reactions are polar, aprotic polar organic solvents are chosen. However, because this reaction competes with protic solvents such as water for substitution, water is not allowed in the system.

[0014] In this invention, the reaction equation for dihalohydrocarbons and alkali metal sulfides (taking sodium sulfide as an example) is as follows: Preferably, the purification includes the following steps: after the nucleophilic substitution reaction is completed, the mixture is sequentially separated, rotary evaporated, filtered, and dried.

[0015] Preferably, the inert atmosphere is a gas atmosphere obtained by mixing at least one gas selected from helium, neon, argon, and nitrogen.

[0016] In this invention, alkali metal sulfides need to be added to toluene solvent together with dihalohydrocarbons, and the influence of moisture on the reaction is eliminated as much as possible by introducing the gas that can form an inert atmosphere in advance.

[0017] Preferably, the molar ratio of the dihalohydrocarbon to the alkali metal sulfide is 1:(2-3). An excess of the alkali metal sulfide ensures the full occurrence of the nucleophilic reaction; within the appropriate range mentioned above, the viscosity of the product is further ensured, facilitating purification operations, especially subsequent liquid-liquid separation.

[0018] Preferably, the dihalohydrocarbon is selected from X-(CH2). n -CH2X, n=6-16, where X represents a halogen, and the halogen is at least one of F, Cl, and Br, with Br being the preferred element.

[0019] Preferably, the alkali metal sulfide includes at least one of sodium sulfide and potassium sulfide.

[0020] Preferably, the concentration of dihalohydrocarbons in the reaction solution is 1.0-2.0 mol / L.

[0021] After the nucleophilic substitution reaction is completed, a capping agent is added for end-capping. Commonly used capping agents in the art can be used for end-capping in this invention. The preferred capping agent is a monothioalkane, which does not introduce impurities and is beneficial to improving the purity of the product.

[0022] In this invention, the nucleophilic substitution reaction is carried out in a closed environment, which is achieved by a closed device containing a reflux pipe.

[0023] In a second aspect, the present invention also provides a sulfur-containing polymer based on a polyethylene backbone, wherein the sulfur-containing polymer based on a polyethylene backbone is prepared by the preparation method described in the first aspect of the present invention.

[0024] In a third aspect, the invention also provides the application of the sulfur-containing polymer based on the polyethylene backbone described in the second aspect of the invention for the preparation of biodegradable mulch films for use in the agricultural field; it can also be used as a drug carrier for the preparation of antitumor drugs.

[0025] Compared with the prior art, the beneficial effects of the present invention are: The preparation method of the present invention uses simple reactants and has low cost in the synthesis process. By adjusting the reaction conditions, the product can be obtained in a one-pot process with only the precursor and solvent of the reactant monomer and without the need for small molecule additives such as end-capping agents and acid-base regulators. This not only reduces the loss caused by multi-step reaction and has a high yield, but also avoids the influence of other reactants on the structure and properties of the product. Attached Figure Description

[0026] Figure 1 Thermogravimetric analysis diagram of the product prepared in Example 1; Figure 2 Differential scanning calorimetry (DSC) of the product prepared in Example 1; Figure 3 The 1H NMR spectra of the product prepared in Example 1 (Figure a) and the product prepared in Comparative Example 8 (Figure b) are shown. Figure 4 The 1H NMR spectra of the products prepared in Example 2 (Figure a) and Example 3 (Figure b) are shown. Figure 5 Thermogravimetric analysis diagram of the product prepared in Comparative Example 8; Figure 6 Differential scanning calorimetry (DSC) of the product prepared in Comparative Example 8; Figure 7 The Fourier transform infrared spectrum of the product prepared in Example 1; Figure 8 The graph shows the degradation performance test results of the product prepared in Example 1. Figure 9 The hydrogen nuclear magnetic resonance spectrum of the product prepared in Comparative Example 1 is shown below. Figure 10 The thermogravimetric analysis diagram is shown for the product prepared in Comparative Example 6. Detailed Implementation

[0027] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0028] Example 1 This embodiment provides a sulfur-containing polymer based on a polyethylene backbone, which is prepared by a method including the following steps: In a closed apparatus containing a reflux tube, 10 mmol of 1,10-dibromodecane, 25 mmol of sodium sulfide, and 10 mL of toluene solvent were mixed thoroughly, and the mixture was purged with nitrogen for 15 min to obtain a reaction solution. Then, a continuous nucleophilic substitution reaction was carried out at 120 °C for 3 days. After standing, separation, rotary evaporation, and filtration, the solution was dried in an oven at 60 °C to constant weight to obtain the sulfur-containing polymer based on the polyethylene backbone.

[0029] The proton NMR spectrum of the product is shown in the figure. Figure 3 The characteristic peak at 2.5 ppm confirms the introduction of sulfur atoms into the polyethylene backbone structure; secondly, thermogravimetric analysis (...) Figure 1 The thermal decomposition temperature of the product can be determined to be 329.79℃.

[0030] Example 2 This embodiment provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that 1,10-dibromodecane is replaced with an equimolar amount of 1,6-dibromohexane.

[0031] Example 3 This embodiment provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that 1,10-dibromodecane is replaced with an equimolar amount of 1,16-dibromohexadecane.

[0032] Example 4 This embodiment provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1. The difference from Example 1 is that the nucleophilic substitution reaction temperature is 140°C and the nucleophilic substitution reaction time is 2 days.

[0033] Example 5 This embodiment provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that the amount of toluene solvent used is 50 mL.

[0034] Example 6 This embodiment provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that the amount of sodium sulfide used is replaced with 30 mmol.

[0035] Comparative Example 1 This comparative example provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that the nucleophilic substitution reaction temperature is 150°C.

[0036] Comparative Example 2 This comparative example provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that the solvent is replaced with xylene.

[0037] Comparative Example 3 This comparative example provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that the solvent toluene is replaced with an equal volume of diethyl ether.

[0038] Comparative Example 4 This comparative example provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that the solvent toluene is replaced with an equal volume of N,N-dimethylformamide.

[0039] Comparative Example 5 This comparative example provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that the solvent toluene is replaced with an equal volume of ethanol.

[0040] Comparative Example 6 This comparative example provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that no solvent is added.

[0041] Comparative Example 7 This comparative example provides a sulfur-containing polymer based on a polyethylene backbone, prepared according to the method of Example 1, except that the nucleophilic substitution reaction temperature is 80°C.

[0042] Comparative Example 8 This comparative example provides a sulfur-containing polymer based on a polyethylene backbone, prepared by a method comprising the following steps: In a closed apparatus containing a reflux tube, 155 mmol of 1,10-dibromodecane, 310 mmol of sodium sulfide, and 140 mmol of sodium carbonate (a pH adjuster) were dissolved in 90 mL of toluene. The mixture was heated to 80 °C and purged with nitrogen for 15 min to obtain a reaction solution. The solution was then subjected to a continuous nucleophilic substitution reaction at 125 °C for 2 days. An end-capping agent was added to cap the solution (capping reaction for about 1 day). After standing, separation, rotary evaporation, and filtration, the solution was dried in an oven at 60 °C to constant weight to obtain the sulfur-containing polymer based on the polyethylene backbone.

[0043] The proton NMR spectrum of the product is shown below. Figure 3 (Figure b) The characteristic peak at 2.5 ppm confirms the introduction of sulfur atoms into the polyethylene backbone structure; secondly, thermogravimetric analysis ( Figure 5The results show that the thermal decomposition temperature of the product is 297.19℃, further confirming the formation of the polyethylene main chain.

[0044] Performance testing The products and their properties obtained in the above embodiments and comparative examples were characterized. The specific test items, test methods, and results are as follows: 1. Structural characterization: (1) Through thermogravimetric analysis, see Figure 1 Taking Example 1 as an example, it is shown that the product almost completely decomposes within the characterization temperature, the inorganic and organic phases are completely separated, and the product has high purity. The product has a high degree of polymerization, therefore the thermal decomposition temperature is also high, approximately 329.79℃.

[0045] The test results of the products of other embodiments are similar to those of Embodiment 1, as detailed in Table 1.

[0046] (2) Results of differential scanning calorimetry (DSC) Figure 2 The results show that the melting point of the product in Example 1 is about 81.95℃ and the crystallization temperature is 68.00℃. The test results of the products in other examples are detailed in Table 1. It can be seen that the melting point of the products prepared by the method of the present invention is also above 67.59℃ and the crystallization temperature is above 55.2℃, which is convenient for subsequent processing into film.

[0047] (3) Fourier transform infrared spectroscopy ( Figure 7 It was observed that the product in Example 1 had functional group signals similar to those of polyethylene, indicating that a polyethylene long-chain structure was successfully synthesized in the product. The test results of other examples were similar.

[0048] (4) Proton nuclear magnetic resonance spectrum: The product dissolved in toluene (i.e., the sulfur-containing polymer based on a polyethylene backbone mentioned above in this invention) can be obtained by separation, rotary evaporation, filtration, and drying. Because the product has a similar structure to polyethylene and a relatively high degree of polymerization, it does not dissolve well in the test solvent deuterated chloroform. Therefore, performing 1H NMR spectroscopy on the product is somewhat difficult, and the measured peak signal (at 2.5 ppm) is rather weak (see...). Figure 3 (a) and no peak signal of bromine terminal group was observed in the product (at 3.4 ppm), indicating that the starting material dibromodecane reacted completely.

[0049] To further confirm the structure of the product, the product obtained in Comparative Example 8 (see...) was analyzed. Figure 3 (b) and Example 2 (see Example 2) Figure 4 (a) The product obtained in Example 3 (see Example 3) Figure 4 (b) As a reference, verify the proton spectrum results of similar structures.

[0050] 2. Application performance testing The products prepared in the above examples and comparative examples were tested using the closed-loop respiration assay (ISO 17556:2019) to analyze carbon dioxide production and oxygen consumption. Under ideal conditions, the biodegradation of plastic materials should achieve complete transformation, with the final products being carbon dioxide, water, and biomass. Specifically, the organic components in plastics are decomposed through microbial metabolism, and carbon is mainly released as carbon dioxide through respiration. Therefore, by measuring the oxygen demand and carbon dioxide production in a closed system, the final aerobic biodegradability of plastics in soil was determined. The degradation rate was expressed as the amount of carbon dioxide produced. The test results are shown in Table 1 and [Table data missing]. Figure 8 (Example 1), from Figure 8 As can be seen, the sulfur-containing polymer degrades the fastest in the first 5 days, which may be due to the loss of impurity salts and small molecules through hydrolysis. The degradation of the product begins to slow down from the 5th day. This stage of degradation is the slow degradation of the sulfur-containing polymer product. In this invention, the degradation rate on the 7th day (when the degradation rate is about to stabilize) was selected for testing. The test results of other embodiments and comparative examples are detailed in Table 1.

[0051] 3. Yield is calculated using the following formula: Yield .

[0052] The test results are detailed in Table 1.

[0053] Table 1 The results above show that: This invention successfully prepared sulfur-containing polymer materials based on a polyethylene backbone with excellent degradation and mechanical properties using a simple method. The yield was also high, exceeding 85%.

[0054] The sulfur-containing polymer materials based on polyethylene backbone of the present invention have crystallization temperatures above 55°C, which facilitates processing; thermal decomposition temperatures above 200°C, which provides excellent thermal stability; and degradation rates above 30 mg CO2 / g polymer / day.

[0055] The reaction temperature in Comparative Example 1 was too high, resulting in a vigorous reaction and causing changes in the product structure (see...). Figure 9 As can be seen from the figure, the signal at 2.5 ppm is very low, and the peak position and intensity of the characteristic peak in the range of 0.6 ppm-1.8 ppm are similar to those of the product in Example 1. Figure 3 (a) is different, so we believe that Comparative Example 1 is not our expected product.

[0056] The results of Example 1 and Comparative Examples 2-5 show that, after the solvent was changed, water and ethanol solvents have nucleophilic ability, so they will compete with thiols for reaction during the long heating process, resulting in reaction failure; diethyl ether and N,N-dimethylformamide do not react because their solubility and boiling point are much different from the reaction raw materials used in this application.

[0057] In Comparative Example 6, no solvent was added, and the reaction was carried out only at high temperature. Although the yield reached over 50%, the resulting product was a viscous paste rather than a powder, and the thermogravimetric analysis showed... Figure 10 As can be seen from the data, the product has multiple decomposition temperatures, indicating that the polymerization in the product is uneven, which prevents the product from forming a film for use.

[0058] In Comparative Example 7, the reaction temperature was lower and the yield was lower.

[0059] In Comparative Example 8, sodium carbonate, an acid-base conditioner, was added, and the reaction underwent two stages of heating. Thermogravimetric analysis was performed to determine the reaction outcome. Figure 5 Differential scanning calorimetry (DSC) Figure 6 ), 1H NMR spectrum ( Figure 3 Figure b in the diagram shows that sulfur-containing polymers based on a polyethylene backbone can be prepared, but from... Figure 3 The comparison of the (H NMR spectra) shows that the product of Comparative Example 8 has a stronger peak of bromine end groups at 3.4 ppm, indicating that more bromine end groups were generated. The molecular weight of the product is reduced, indicating that the reaction efficiency is low and the polymer chain cannot grow effectively.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a sulfur-containing polymer based on a polyethylene skeleton, characterized in that: The steps include: The dihalogenated hydrocarbon and alkali metal sulfide are dissolved in toluene to obtain a reaction solution, and then a continuous nucleophilic substitution reaction is carried out in an inert atmosphere at 120-140° C. for 48-96 hours. After purification, the sulfur-containing polymer based on the polyethylene skeleton can be obtained.

2. The method for preparing a sulfur-containing polymer based on a polyethylene skeleton according to claim 1, characterized in that: The molar ratio of the dihalogenated hydrocarbon to the alkali metal sulfide is 1:(2-3).

3. The method for preparing a sulfur-containing polymer based on a polyethylene skeleton according to claim 1, characterized in that: In the reaction solution, the concentration of dihalogenated hydrocarbon is 1.0-2.0 mol / L.

4. The method for preparing a sulfur-containing polymer based on a polyethylene skeleton according to claim 1, characterized in that: The dihalogenated hydrocarbon is selected from X-(CH2) n -X, n=6-16, X represents a halogen, and the halogen is at least one of F, Cl, and Br elements.

5. The method for preparing a sulfur-containing polymer based on a polyethylene skeleton according to claim 1, characterized in that: The alkali metal sulfide includes at least one of sodium sulfide and potassium sulfide.

6. The method for preparing a sulfur-containing polymer based on a polyethylene skeleton according to claim 1, characterized in that: The nucleophilic substitution reaction is carried out in a closed environment.

7. The method for preparing a sulfur-containing polymer based on a polyethylene skeleton according to claim 1, characterized in that: After the nucleophilic substitution reaction is completed, a capping agent is added for capping.

8. The method for preparing a sulfur-containing polymer based on a polyethylene skeleton according to claim 1, characterized in that: The purification comprises the following steps: after the nucleophilic substitution reaction is completed, liquid separation, rotary evaporation, suction filtration and drying are performed in sequence.

9. A sulfur-containing polymer based on a polyethylene skeleton, characterized in that: The polymer is prepared according to the method for preparing a sulfur-containing polymer based on a polyethylene skeleton according to any one of claims 1 to 8.

10. An application of the sulfur-containing polymer based on a polyethylene skeleton according to claim 9, characterized in that: The sulfur-containing polymer based on the polyethylene skeleton is used for preparing ground films and drug carriers.

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