Preparation method of dynamic cross-linked polymer based on hindered urea bond

Abstract

The invention focuses on the field of recoverable polymer materials, and discloses a preparation method of a dynamic cross-linked polymer based on a hindered urea bond. According to the method, dynamic cross-linking modification is carried out on the basis of thermoplastic general-purpose plastics, and a dynamic cross-linked network formed by reaction of maleic anhydride, aziridine, isophorone diisocyanate and the like is introduced. In a dynamic cross-linked network, a group adjacent to a urea bond is used as a steric hindrance structure to reduce the stability of the urea bond, so that the cross-linked polymer is endowed with a good dynamic bonding characteristic. Under a specific heating condition, the cross-linked polymer can be subjected to urea bond exchange reaction and shows melt processability. The cross-linked polymer has good solvent resistance, creep resistance and tensile modulus, and also has good melt processability, recoverability and self-repairability.

Description

Technical Field

[0001] The invention relates to a preparation method of a dynamic cross-linked polymer based on hindered urea bonds, and belongs to the field of recyclable polymer materials. Background Art

[0002] Plastics are cheap, lightweight and often stronger than natural materials, making them part of everyday life.

[0005] In order to realize the circular economy of plastics, the recyclable modification technology of plastics is regarded as the key to promoting the recycling of plastics. Among them, the concept of dynamic covalent bonds provides a potential modification path for the high-quality recycling of plastics. Despite this, the technology still faces many difficulties in its implementation, such as insufficient selectivity in the chemical recycling process, balanced regulation of monomer and polymer cycles, easy deactivation of catalysts and high costs. Therefore, it is necessary to develop a modification method based on general-purpose plastics (or bulk plastics) to achieve dynamic cross-linking modification of general-purpose plastics without the need for catalysts, which not only improves its comprehensive performance, but also ensures that the material can maintain good performance after multiple recycling processes, thereby realizing the recycling of plastics. Summary of the invention

[0006] Purpose of the invention: Aims to provide a method for preparing a dynamically cross-linked polymer based on hindered urea bonds. The method converts linear thermoplastic general-purpose plastics into polymer materials with a network-like cross-linked structure through dynamic cross-linking modification technology. Due to this modification, the resulting dynamically cross-linked polymer exhibits enhanced solvent resistance, room temperature creep resistance, and tensile modulus, as well as good melt processability, recyclability, and self-healing properties, and the mechanical properties after recycling or self-healing are comparable to those of the initial product.

[0007] Technical solution: In order to achieve the above-mentioned purpose, the method for preparing a dynamically cross-linked polymer based on hindered urea bonds described in the present invention comprises the following steps:

[0008] Step 1: In N,N-dimethylformamide (DMF) solvent, thermoplastic general-purpose plastic, maleic anhydride (MA), and benzoyl peroxide (BPO) are mixed in a specific mass ratio and reacted in a nitrogen atmosphere at 80°C for 4 hours. The mass ratio of thermoplastic general-purpose plastic to maleic anhydride is controlled at (30-100):1, and the mass ratio of maleic anhydride to benzoyl peroxide is (5-20):1;

[0009] Step 2: Add deionized water dropwise and continue stirring for 2 hours to promote the hydrolysis of the anhydride into carboxylic acid. Then add a stoichiometric amount of aziridine and continue the reaction at 80°C for 3 hours to introduce active hydrogen reaction sites;

[0010] Step 3: directly add stoichiometric isophorone diisocyanate without additional catalyst, react for 2 hours, pour the resulting mixture into a polytetrafluoroethylene mold, dry it in a nitrogen atmosphere at 120°C for 5 hours, and then cool it to room temperature to obtain a dynamically cross-linked polymer;

[0011] Step 4: The discarded dynamically cross-linked polymer is placed in an environment of 120-170°C and reprocessed using a specific polymer processing method (including hot pressing, micro injection molding, 3D printing, casting, and extrusion), and the material properties can be maintained.

[0012] In the above step 1, the thermoplastic general-purpose plastic is preferably polyethylene, polypropylene, polybutadiene, polyisoprene, polystyrene, polyacrylate, polylactic acid, polyacrylonitrile-polybutadiene-polystyrene (ABS) copolymer or blend, used alone or in combination.

[0013] In the above step 2, the aziridine is preferably one or more of the following compounds: 1-(triphenylmethyl)-2-aziridinecarboxylic acid methyl ester, trimethylolpropane tris[3-(2-methylaziridine-1-yl) propionate], 2-phenylaziridine, aziridine-2-carboxylic acid methyl ester, S-2-benzylaziridine, aziridine-1-carboxylic acid benzyl ester, cis-1,2,3-triphenylaziridine, cis-2,3-diphenyl-1-propylaziridine, 2-formyl-1-trityl-aziridine, (R)-2-methylaziridine-1-carboxylic acid tert-butyl ester, cis-1-isopropyl-2,3-diphenylaziridine, and trans-1-isopropyl-2,3-diphenylaziridine.

[0014] The beneficial effects are as follows: (1) The present invention successfully transforms linear thermoplastic general-purpose plastics into a network-like cross-linked structure through dynamic cross-linking technology, significantly improving its solvent resistance, creep resistance, and mechanical properties, and broadening its application range. (2) The prepared dynamically cross-linked polymer has excellent recyclability and can be repeatedly recycled through urea bond exchange reaction at a specific temperature, which not only reduces resource waste and environmental pollution, but also maintains the performance of the polymer material after multiple cycles, showing good sustainability and economy. Dynamic cross-linking breaks through the limitation that the conventional cross-linked polymer network structure cannot be melt-processed and recycled once it is formed, which is conducive to sustainable development and circular economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The schematic diagram of the synthesis process and chemical structure of the dynamically cross-linked polymer ABS-V of Example 1;

[0016] Figure 2The compression molding schematic diagram and product photo of the hot pressing recycling of the dynamically cross-linked polymer ABS-V in Example 1;

[0017] Figure 3 Schematic diagram of micro injection molding of dynamically cross-linked polymer ABS-V and photos of injection molded products in Example 1;

[0018] Figure 4 Schematic diagram of 3D printing of dynamically cross-linked polymer ABS-V and photos of printed products in Example 1;

[0019] Figure 5 Schematic diagram of the casting mold and product photo of the dynamically cross-linked polymer ABS-V of Example 1;

[0020] Figure 6 The extrusion schematic diagram and extrusion product photo of the dynamically cross-linked polymer ABS-V of Example 1;

[0021] Figure 7 The dynamically cross-linked polymer ABS-V of Example 1 was immersed in N,N-dimethylformamide at 60° C. for 7 days;

[0022] Figure 8 The dynamically cross-linked polymer ABS-V of Example 1 was immersed in ethyl acetate at 60° C. for 7 days;

[0023] Fig. 9 The stress-strain curves of the dynamically cross-linked polymer ABS-V of Example 1 at different cross-linking degrees;

[0024] Fig.10 The creep resistance of the dynamically cross-linked polymer ABS-V of Example 1 at room temperature;

[0025] Fig.11 The stress relaxation behavior of the dynamically cross-linked polymer ABS-V at different temperatures in Example 1;

[0026] Fig.12 The stress-strain curve of the dynamically cross-linked polymer ABS-V in Example 1 after direct synthesis and recycling;

[0027] Fig.13 The thermal stability of the dynamically cross-linked polymer ABS-V in Example 1 after direct synthesis and recycling;

[0028] Fig.14 This is a test of the mechanical properties of the dynamically cross-linked polymer ABS-V of Example 1 after self-repair. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0030] The raw materials and equipment used in the present invention can be purchased from the market or are commonly used in the art, and the methods in the embodiments are all conventional methods in the art. Unless otherwise specified, parts are all weight parts, temperatures are all expressed in ° C or at ambient temperature, and pressures are atmospheric pressure. There are many combinations of reaction conditions (such as component concentrations, solvents, solvent mixtures, temperature, pressure, etc.) and conditions that can be used to optimize chemical reaction purity and yield, and only reasonable routine experiments will be required to optimize such combinations.

[0031] Example 1

[0032] A method for preparing a dynamically cross-linked polymer based on hindered urea bonds, comprising the following steps:

[0033] Step 1: 50 g of polyacrylonitrile-polybutadiene-polystyrene (ABS) copolymer resin, 1 g of maleic anhydride (MA) and 0.1 g of benzoyl peroxide (BPO) were mixed in 200 ml of N,N-dimethylformamide (DMF) solvent and reacted at 80° C. in a nitrogen atmosphere for 4 hours;

[0034] Step 2: add 0.5 g of deionized water dropwise and stir for 2 hours, then add a stoichiometric amount of aziridine and react at 80 °C for 3 hours;

[0035] Step 3: Add stoichiometric amount of isophorone diisocyanate (IPDI), react for 2 hours, pour the mixture into a polytetrafluoroethylene mold, and dry it in an oven in a nitrogen atmosphere at 120° C. for 5 hours to finally obtain a dynamically cross-linked polymer ABS-V.

[0036] Figure 1 The schematic diagram of the synthesis process and chemical structure of the dynamic cross-linked polymer ABS-V. The trityl structure of aziridine acts as a steric hindering group adjacent to the urea bond, which can reduce the binding stability of the urea bond, allowing it to undergo a urea bond exchange reaction after heating to a certain temperature, prompting the topological rearrangement of the entire cross-linked polymer network structure. From a macroscopic perspective, the polymer has good melt processing properties.

[0037] Figure 2 Dynamically cross-linked polymer ABS-V was recycled by hot pressing. The obtained products reflected good product quality and uniformity, proving that ABS-V has good reprocessability.

[0038] Figure 3 Dynamically cross-linked polymer ABS-V was recycled by micro injection molding. The obtained products reflected good product quality and uniformity, proving that ABS-V has good reprocessability.

[0039] Figure 4The dynamically cross-linked polymer ABS-V was recycled through 3D printing. The obtained products reflected good product quality and uniformity, proving that ABS-V has good reprocessability.

[0040] Figure 5 Dynamically cross-linked polymer ABS-V was recycled by casting. The obtained products reflected good product quality and uniformity, proving that ABS-V has good reprocessability.

[0041] Figure 6 The dynamically cross-linked polymer ABS-V was recycled by extrusion. The obtained products reflected good product quality and uniformity, proving that ABS-V has good reprocessability.

[0042] Figure 7 The solvent resistance test of the dynamically cross-linked polymer ABS-V and the initial ABS. After being immersed in N,N-dimethylformamide at 60°C for 7 days, ABS-V only swelled, while ABS was completely dissolved, proving the formation of a cross-linked structure in ABS-V and its better solvent resistance.

[0043] Figure 8 The solvent resistance test of the dynamically cross-linked polymer ABS-V and the initial ABS. After being immersed in ethyl acetate at 60°C for 7 days, ABS-V only swelled, while ABS was completely dissolved, proving the formation of a cross-linked structure in ABS-V and its better solvent resistance.

[0044] Fig. 9 The room temperature tensile properties of dynamically cross-linked polymer ABS-V and initial ABS with different cross-linking degrees were tested. Compared with initial ABS, dynamic cross-linking significantly improved the mechanical properties of ABS-V, with its Young's modulus and tensile strength reaching 720±87MPa and 41±2.9MPa respectively, enhancing the polymer's ability to resist deformation due to external forces.

[0045] Fig.10 This is a creep resistance test of dynamically cross-linked polymer ABS-V and initial ABS at room temperature. After applying 1MPa stress for 10 minutes and then removing it, the strain of ABS-V is smaller and most of it can be recovered, showing better creep resistance and ability to resist external damage.

[0046] Fig.11 This is a stress relaxation test of the dynamically cross-linked polymer ABS-V. ABS-V can undergo complete stress relaxation above 130°C, showing the viscoelastic characteristics of a linear thermoplastic polymer, indicating that it can trigger the exchange reaction of the urea bond when the temperature rises to a certain level, thereby achieving rearrangement.

[0047] Fig.12The mechanical properties of the dynamically cross-linked polymer ABS-V were tested after three recycling processes. After multiple recycling of ABS-V fragments by hot pressing at 150°C, the tensile strength was 41±1.1MPa, which was comparable to that of the initially synthesized ABS-V sample, with no performance degradation.

[0048] Fig.13 This is a test of the thermal weight loss performance of the dynamically cross-linked polymer ABS-V after recycling. ABS-V will not undergo thermal decomposition at the processing temperature, and its thermal stability is still maintained after multiple recycling and reprocessing.

[0049] Fig.14 This is a test of the mechanical properties of the self-repaired samples of the dynamically cross-linked polymer ABS-V after fracture. After being damaged by external forces, ABS-V can achieve effective self-repair by splicing, and the mechanical properties of the repaired samples are comparable to those of the initial synthesized samples.

[0050] Example 2

[0051] A method for preparing a dynamically cross-linked polymer based on hindered urea bonds, comprising the following steps:

[0052] Step 1: 50 g of isoprene resin, 1 g of maleic anhydride (MA) and 0.1 g of benzoyl peroxide (BPO) were mixed in 200 ml of N,N-dimethylformamide (DMF) solvent and reacted at 80° C. under a nitrogen atmosphere for 4 hours;

[0053] Step 2: add 0.5 g of deionized water dropwise and stir for 2 hours, then add a stoichiometric amount of aziridine and react at 80 °C for 3 hours;

[0054] Step 3: Add stoichiometric isophorone diisocyanate (IPDI) and react for 2 hours, then pour the mixture into a polytetrafluoroethylene (PTFE) mold and dry it in an oven in a nitrogen atmosphere at 120° C. for 5 hours to obtain a dynamically cross-linked polymer.

[0055] Similar to Example 1, the obtained dynamically cross-linked polymer exhibits enhanced solvent resistance, room temperature creep resistance, and tensile modulus, and also exhibits good melt processability, recyclability, and self-healing properties. The mechanical properties after recycling or self-healing are comparable to those of the initial product.

Claims

1. A method for preparing a dynamically cross-linked polymer based on hindered urea bonds, characterized in that: The steps include: Step a: In N,N-dimethylformamide solvent, thermoplastic general-purpose plastic, maleic anhydride and benzoyl peroxide are mixed in a specific mass ratio and reacted at 80° C. in a nitrogen atmosphere for 4 hours; Step b: Add deionized water dropwise and continue stirring for 2 hours to promote the hydrolysis of the anhydride into carboxylic acid. Then add a stoichiometric amount of aziridine and continue the reaction at 80°C for 3 hours to introduce active hydrogen reaction sites; Step c: directly adding a stoichiometric amount of isophorone diisocyanate, reacting for 2 hours, pouring the resulting mixture into a polytetrafluoroethylene mold, drying it under a nitrogen atmosphere at 120° C. for 5 hours, and then cooling it to room temperature to obtain a dynamically cross-linked polymer; Step d: The discarded dynamically cross-linked polymer is placed in a reprocessing temperature environment and reprocessed using a specific polymer processing method.

2. The method for preparing a dynamically cross-linked polymer based on hindered urea bonds according to claim 1, characterized in that: The general-purpose thermoplastic plastic is selected from one or more of polyethylene, polypropylene, polybutadiene, polyisoprene, polystyrene, polyacrylate, polylactic acid, and polyacrylonitrile-polybutadiene-polystyrene copolymer or blend.

3. The method for preparing a dynamically cross-linked polymer based on hindered urea bonds according to claim 1, characterized in that: The aziridine is selected from one or more of the following compounds: 1-(triphenylmethyl)-2-aziridinecarboxylic acid methyl ester, trimethylolpropane tris[3-(2-methylaziridine-1-yl) propionate], 2-phenylaziridine, aziridine-2-carboxylic acid methyl ester, S-2-benzylaziridine, aziridine-1-carboxylic acid benzyl ester, cis-1,2,3-triphenylaziridine, cis-2,3-diphenyl-1-propylaziridine, 2-formyl-1-trityl-aziridine, (R)-2-methylaziridine-1-carboxylic acid tert-butyl ester, cis-1-isopropyl-2,3-diphenylaziridine, and trans-1-isopropyl-2,3-diphenylaziridine.

4. The method for preparing a dynamically cross-linked polymer based on hindered urea bonds according to claim 1, characterized in that: In step a, the mass ratio of the thermoplastic general-purpose plastic to maleic anhydride is controlled at (30-100):1, and the mass ratio of maleic anhydride to benzoyl peroxide is controlled at (5-20):

1.

5. The method for preparing a dynamically cross-linked polymer based on hindered urea bonds according to claim 1, characterized in that: In step d, the reprocessing temperature is 120-170°C.

6. The method for preparing a dynamically cross-linked polymer based on hindered urea bonds according to claim 1, characterized in that: In step d, the specific polymer processing and molding method includes hot pressing molding, micro injection molding, 3D printing molding, casting molding, and extrusion molding.

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