Composite catalyst and method for chemical recovery of polymethacrylate polymer

Abstract

The invention provides a composite catalyst and a method for chemical recovery of a polymethacrylate polymer, and belongs to the technical field of high polymer materials. The composite catalyst for chemical recovery of the polymethacrylate polymer comprises a trivalent iron salt, a quaternary ammonium salt chelating agent and a triphenylphosphino conjugated super-crosslinked polymer with a layered porous structure, the triphenylphosphino conjugated super-crosslinked polymer is prepared from triphenylphosphine and an aromatic monomer through a Friedel-Crafts alkylation reaction under the catalytic action of a Lewis acid catalyst.

Description

Technical Field

[0001] This disclosure relates to the field of polymer materials technology, and in particular to a composite catalyst and method for the chemical recycling of polymethacrylate polymers. Background Technology

[0002] Polymethyl methacrylate polymers, with their excellent transparency, mechanical properties, and stable chemical properties, are widely used in various fields such as medical devices, optical devices, and 3D printing. However, the stable carbon-carbon backbone structure of these polymers makes them difficult to degrade naturally. Traditional disposal methods, mainly landfilling and incineration, not only violate the concept of a circular economy and waste resources, but also cause environmental problems such as microplastic pollution and greenhouse gas emissions.

[0003] Currently, the main methods for recycling plastic waste include mechanical recycling, physical recycling, chemical recycling, and biodegradation. Among them, chemical recycling is considered an ideal approach for the sustainable development of polymethyl methacrylate polymers because of its higher monomer recovery rate and purity, lower energy consumption, strong adaptability to complex waste materials, and the ability of recovered monomers to be used in high-end applications rather than for downgrading.

[0004] In recent years, catalytic depolymerization technology has attracted widespread attention due to its ability to increase reaction rates and reduce energy consumption at lower temperatures. However, existing catalytic systems have several drawbacks: homogeneous catalysts are difficult to separate and recover and are prone to product contamination; heterogeneous catalysts, while easy to separate, suffer from poor accessibility of active sites and low catalytic efficiency. Furthermore, the main chain breakage pathways in existing catalytic systems are difficult to guide depolymerization and regeneration of the original monomers, resulting in low monomer recovery rates and products that are mostly complex low-molecular-weight aliphatic mixtures, failing to meet the requirements for recycling and repolymerization. Summary of the Invention

[0005] In view of this, the main objective of this disclosure is to provide a composite catalyst and method for the chemical recovery of polymethacrylate polymers, in order to at least partially solve at least one of the aforementioned technical problems.

[0006] To achieve the above objectives, the technical solution disclosed herein is as follows:

[0007] In one aspect of this disclosure, a composite catalyst for the chemical recovery of polymethacrylate polymers is provided, comprising a trivalent iron salt, a quaternary ammonium salt chelating agent, and a layered porous triphenylphosphine-based conjugated hypercrosslinked polymer, wherein the triphenylphosphine-based conjugated hypercrosslinked polymer is prepared by a Friedel-Crafts alkylation reaction of a photochemically active monomer containing triphenylphosphine and dimethoxybenzene under the catalysis of a Lewis acid catalyst.

[0008] In some embodiments, the ferric salt includes any one of ferric chloride, sodium tetrachloroferrate, and ammonium tetrachloroferrate; the chelating agent includes any one of tetrabutylammonium bromide and tetrabutylammonium chloride.

[0009] In some embodiments, the triphenylphosphine-based conjugated hypercrosslinked polymer has a particle size of 40-60 μm and a pore size of 1-3 nm.

[0010] In some embodiments, the preparation method of the triphenylphosphine-based conjugated hypercrosslinked polymer includes: dissolving a photochemically active monomer containing triphenylphosphine and dimethoxybenzene in an organic solvent with a Lewis acid catalyst to form a mixed solution; performing a Friedel-Crafts alkylation reaction under inert gas protection and at a temperature of 80-140°C to obtain a polymer precursor; and dispersing the polymer precursor in a solution containing a reducing agent under a nitrogen atmosphere for reduction treatment to obtain the triphenylphosphine-based conjugated hypercrosslinked polymer.

[0011] In some embodiments, the photochemically active monomer containing triphenyl includes any one of triphenylphosphine and triphenylphosphine oxide; the Lewis acid catalyst is anhydrous ferric chloride; and the reducing agent includes any one of sodium borohydride, sodium triacetoxyborohydride, sodium chloride, calcium chloride, potassium chloride, sodium bromide, potassium bromide, lithium bromide, sodium iodide, lithium iodide, and potassium iodide.

[0012] In another aspect of this disclosure, a chemical recovery method for polymethyl methacrylate polymers is provided, comprising: adding the above-mentioned composite catalyst and polymethyl methacrylate polymers into an organic solvent to obtain a mixed solution; deoxygenating the mixed solution; heating the deoxygenated mixed solution to 80~160°C in an oxygen-free environment to cause the polymethyl methacrylate polymers to undergo a depolymerization reaction; and recovering the methyl methacrylate monomers after separation and purification.

[0013] In some embodiments, the molar ratio of trivalent iron salt to quaternary ammonium salt chelating agent is 1:0.01 to 1:100, preferably 1:0.1 to 10; the amount of triphenylphosphine-based conjugated hypercrosslinked polymer is 1 to 10 mg / mL.

[0014] In some embodiments, the molar ratio of polymethacrylate polymer to ferric ions in the composite catalyst is 1:0.1~10.

[0015] In some embodiments, the polymethacrylate polymer is any one of polymethyl methacrylate, polybutyl methacrylate, and benzyl methacrylate; the concentration of the polymethacrylate polymer in the organic solvent is 50~2000mM; the organic solvent includes any one of acetonitrile, acetone, dichlorobenzene, dimethyl sulfoxide, N,N-dimethylformamide, n-butanol, and xylene.

[0016] In some embodiments, the recovery method further includes: after the depolymerization reaction is completed, separating the triphenylphosphine-based conjugated hypercrosslinked polymer from the composite catalyst, and washing and drying the triphenylphosphine-based conjugated hypercrosslinked polymer for recovery.

[0017] According to embodiments of this disclosure, a composite catalyst for the chemical recovery of polymethyl methacrylate polymers is provided, comprising a ferric salt, a quaternary ammonium salt chelating agent, and a layered porous triphenylphosphine-based conjugated hypercrosslinked polymer. The ferric salt serves as the active center of the composite catalyst, initiating the breaking of carbon-carbon bonds in the polymerization of polymethyl methacrylate polymers, thus laying the foundation for the depolymerization reaction. The quaternary ammonium salt chelating agent modulates the iron ion structure in the ferric salt and promotes the mass transfer process, enhancing the reaction kinetics. The layered porous triphenylphosphine-based conjugated hypercrosslinked polymer combines the functions of a support and a synergistic catalytic agent. Its high specific surface area and layered structure stabilize and fix the active components in the catalyst, improving the accessibility of active sites. Furthermore, its electron-rich triphenylphosphine groups can form electronic interactions with the iron ions in the ferric salt, further enhancing the catalytic activity. The catalytic system constructed by the three components can achieve efficient depolymerization of polymethyl methacrylate polymers at relatively low temperatures (80~160℃). Furthermore, the triphenylphosphine-based conjugated hypercrosslinked polymer is a solid porous material, which can be separated from the liquid products and solvents by simple filtration or centrifugation after the reaction, enabling the catalyst to be recycled. Overall, it has good prospects for industrial application. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the triphenylphosphine-based conjugated hypercrosslinked polymer in Example 1;

[0019] Figure 2 The UV-Vis absorption spectrum of the triphenylphosphine-based conjugated hypercrosslinked polymer in Example 1 is shown below.

[0020] Figure 3 The above is the 1H NMR spectrum of the benzyl methacrylate monomer formed by depolymerization of polymethyl methacrylate in Example 1 of this disclosure via chemical recycling method;

[0021] Figure 4 The above is a hydrogen NMR spectrum of the methyl methacrylate monomer formed after depolymerization of polymethyl methacrylate by chemical recycling method in Example 2.

[0022] Figure 5 The 1H NMR spectrum of the butyl methacrylate monomer formed after depolymerization of polybutyl methacrylate by chemical recycling method in Example 3 is disclosed. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0024] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0026] Polymethacrylate polymers are widely used in various fields due to their high transparency, good mechanical properties, and stability. However, the strong stability of their carbon-carbon (CC) backbone structure makes natural degradation difficult. Traditional landfill and incineration methods are wasteful of resources, pollute the environment, and cause microplastic pollution and greenhouse gas emissions. Chemical recycling is an ideal way to sustainably recycle these polymers, but existing catalytic depolymerization technologies face many bottlenecks: homogeneous catalysts are difficult to separate and recover and easily contaminate the products; heterogeneous catalysts have poor accessibility of active sites and low catalytic efficiency; existing systems have low monomer recovery rates, and the products are mostly complex low-molecular-weight mixtures, which are difficult to meet the requirements for repolymerization; moreover, the reaction requires a high-temperature (above 160°C) and low-concentration environment, and some processes rely on polluting chlorinated solvents, limiting their environmental friendliness and practicality.

[0027] Therefore, there is an urgent need to provide a novel catalytic system that can efficiently catalyze the depolymerization of polymethyl methacrylate polymers under relatively mild conditions and is easy to recycle and separate, which has practical application value for alleviating the problem of waste plastic recycling.

[0028] Based on this, this application provides a composite catalytic system with synergistic effects of "active center-regulating component-functional carrier" to solve the above-mentioned technical problems. Specifically, it is achieved through a combination of ferric salt, quaternary ammonium salt chelating agent, and triphenylphosphine-based conjugated hypercrosslinked polymer (PPh3-CHCP). The ferric salt serves as the catalytically active core, inducing homolytic cleavage of chemical bonds in the polymethyl methacrylate polymer chain through single-electron transfer, thereby inducing CC backbone breakage. The quaternary ammonium salt chelating agent can form active complexes with iron ions in the ferric salt, regulating its electronic structure and reactivity, while also playing a phase transfer role to promote mass transfer. PPh3-CHCP, as a heterogeneous carrier, fixes and disperses the active component due to its layered porous structure and high specific surface area. Its electron-rich triphenylphosphine groups can also generate electronic interactions with iron ions in the ferric salt to optimize catalytic performance. The three components work synergistically to achieve highly efficient and selective depolymerization. This composite catalyst enables the depolymerization of various polymers, including polymethyl methacrylate (PMMA), polybutyl methacrylate (PMA), and benzyl methacrylate (BMA), at a mild reaction temperature of 80–160 °C. The depolymerization rate of PMA can reach 90%, with high monomer purity that can be directly used in subsequent high-end applications. Furthermore, PPh3-CHCP can be recycled through simple filtration or centrifugation. The preparation and application of this composite catalyst are simple, energy-efficient, and environmentally friendly, providing a feasible path for industrial-scale promotion.

[0029] According to one aspect of the present disclosure, a composite catalyst for the chemical recovery of polymethacrylate polymers is provided, comprising a trivalent iron salt, a quaternary ammonium salt chelating agent, and a layered porous triphenylphosphine-based conjugated hypercrosslinked polymer, wherein the triphenylphosphine-based conjugated hypercrosslinked polymer is prepared by a Friedel-Crafts alkylation reaction of a photochemically active monomer containing triphenylphosphine and dimethoxybenzene under the catalysis of a Lewis acid catalyst.

[0030] According to embodiments of this disclosure, a catalytic system synergistically constructed from trivalent iron salts, quaternary ammonium salt chelating agents, and layered porous triphenylphosphine-based conjugated hypercrosslinked polymers achieves optimization in multiple aspects, including catalytic performance, recovery efficiency, and reaction compatibility, significantly improving the depolymerization efficiency and monomer selectivity of polymethyl methacrylate polymers.

[0031] Ferric salts serve as the core of the composite catalyst's catalytic activity, initiating the depolymerization reaction of polymethyl methacrylate polymers through a single-electron transfer mechanism. First, the ferric salt transfers a single electron to the heteroatom-containing CX bond (a carbon-halogen bond formed by initiator residues during polymerization, such as C-Cl or C-Br bonds) in the polymer molecule, initiating homolytic cleavage of the CX bond. This homolytic cleavage generates two active intermediates: a carbon-centered free radical with unpaired electrons and an iron-coordinated halide ion that forms a stable coordination structure with the ferric ion. The highly reactive carbon-centered free radical further attacks the stable C-C bonds on the polymer backbone, breaking the chemical bonds and inducing C-C bond breakage. This provides the driving force for the gradual degradation of the long-chain polymer into smaller monomers, ensuring the initiation of the depolymerization reaction from its source.

[0032] Quaternary ammonium salt chelating agents can bind with ferric ions (Fe3+) in ferric salts. 3+ Further synergistic effects are formed: on the one hand, the chelating agent coordinates with Fe through coordination. 3+ The formation of stable active complexes regulates the electron cloud density and coordination environment of iron centers at the molecular level, thus optimizing Fe. 3+ The catalytic activity of the chelating agent is enhanced, and the reaction selectivity is improved. This effectively avoids the catalytic efficiency decay caused by the instability of the electronic state of iron ions and reduces the occurrence of side reactions such as non-directional bond breaking. On the other hand, the quaternary ammonium salt chelating agent has phase transfer catalytic properties, which can improve the compatibility of polymethyl methacrylate polymers with reaction media (such as acetonitrile), improve the solubility and dispersion uniformity of polymers in solvents, break down the mass transfer barriers between polymers and active centers and reaction intermediates, accelerate the contact and interaction of various reactants, and make the catalytic depolymerization reaction proceed more efficiently and smoothly.

[0033] The layered stacked structure and high specific surface area of ​​the triphenylphosphine-based conjugated hypercrosslinked polymer (PPh3-CHCP) provide ample and stable loading sites for the active components formed by ferric salts and chelating agents, ensuring uniform dispersion of the active components and preventing the burial of active sites due to aggregation. Simultaneously, the spatial advantage of the layered structure enhances the exposure and accessibility of active sites, making it easier for polymethyl methacrylate polymers and the active centers of the composite catalyst to react. Furthermore, the electron-rich triphenylphosphine groups in the PPh3-CHCP structure can form strong electronic interactions with ferric centers, further optimizing catalytic activity by regulating the electron cloud density and coordination environment of the iron centers. This results in a highly efficient synergistic catalytic effect with ferric salts and quaternary ammonium salt chelating agents, enhancing overall catalytic efficiency.

[0034] According to embodiments of this disclosure, the trivalent ferric salt includes any one of ferric chloride (FeCl3), sodium tetrachloroferrate (NaFeCl4), and ammonium tetrachloroferrate (NH4FeCl4). All of the above trivalent ferric salts possess stable Fe... 3+ Active center, Fe 3+ Through a single-electron transfer process, long-chain polymers can be progressively degraded, ultimately transforming into the original monomers and providing a driving force for the depolymerization reaction. Simultaneously, these iron salts are chemically stable, widely available, and exhibit good compatibility with chelating agents and triphenylphosphine-based conjugated hypercrosslinked polymers in acetonitrile solvents, fully leveraging their synergistic catalytic effect and preventing the deactivation of active components.

[0035] Quaternary ammonium salt chelating agents include either tetrabutylammonium bromide or tetrabutylammonium chloride. These quaternary ammonium salt chelating agents possess both coordination ability and phase transfer properties, on the one hand reacting with Fe... 3+ This process forms active complexes, modulates the electronic structure and reactivity of the iron center, avoids catalytic efficiency decay and side reactions, and improves depolymerization selectivity. On the other hand, it improves the compatibility with solvents during the recovery of polymethyl methacrylate polymers, promotes mass transfer, overcomes kinetic limitations, and enhances the synergistic catalytic effect among the three components: ferric salt, quaternary ammonium salt chelating agent, and triphenylphosphine-based conjugated hypercrosslinked polymer. Furthermore, this type of chelating agent exhibits strong stability and is not easily decomposed at reaction temperatures of 80–160°C, and is easily separated from the product without affecting the purity of the monomer after final depolymerization.

[0036] According to embodiments of this disclosure, the triphenylphosphine-based conjugated hypercrosslinked polymer (PPh3-CHCP) has a particle size of 40-60 μm, such as 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc.; and a pore size of 1-3 nm, such as 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, etc. The particle size and pore size design provides structural support for PPh3-CHCP to perform its carrier function and synergistic catalytic effect: the appropriate particle size range can effectively avoid polymer particle agglomeration, ensure its uniform dispersion in the reaction system, ensure full exposure of active sites, and facilitate rapid separation and recycling of liquid products and solvents after the reaction through simple filtration or centrifugation; the pore size of 1~3nm can provide suitable loading space for the active components formed by trivalent iron salts and chelating agents such as tetrabutylammonium bromide and tetrabutylammonium chloride, so as to achieve stable fixation and uniform distribution of active components and avoid agglomeration and burying of active sites. At the same time, it can match the size of polymethyl methacrylate polymers and reaction intermediates, ensuring effective contact and rapid mass transfer with active sites, and further promoting the efficient and directional depolymerization reaction.

[0037] According to embodiments of this disclosure, a method for preparing a triphenylphosphine-based conjugated hypercrosslinked polymer includes: dissolving a photochemically active monomer containing triphenylphosphine and dimethoxybenzene in an organic solvent with a Lewis acid catalyst to form a mixed solution; performing a Friedel-Crafts alkylation reaction under inert gas protection and at a temperature of 80-140°C to obtain a polymer precursor; and dispersing the polymer precursor in a solution containing a reducing agent under a nitrogen atmosphere for reduction treatment to obtain a triphenylphosphine-based conjugated hypercrosslinked polymer.

[0038] According to embodiments of this disclosure, a mixed solution containing a photochemically active monomer of triphenylphosphine, dimethoxybenzene, and a Lewis acid catalyst is heated under an inert gas atmosphere to undergo a Friedel-Crafts alkylation reaction. The Lewis acid catalyst promotes the electrophilic substitution reaction between the photochemically active monomer containing triphenylphosphine and dimethoxybenzene, forming carbon-carbon crosslinks. The planar conjugation of the benzene ring of dimethoxybenzene tends to form a layered stacked morphology during crosslinking polymerization. Furthermore, due to the differences in molecular shape and spatial configuration between the photochemically active monomer containing triphenylphosphine and dimethoxybenzene, as well as the randomness of the number and position of crosslinking points during the Friedel-Crafts alkylation reaction, an initial porous structure naturally forms within the three-dimensional network, thereby constructing a polymer precursor (PPh) with a three-dimensional network structure. The preparation process involves using a triphenylphosphine-based conjugated hypercrosslinked polymer (PPh3-CHCP) under inert gas protection to prevent oxygen interference with the reaction process and to prevent oxidation of monomers or products. Subsequently, under a nitrogen atmosphere, the polymer precursor is dispersed in a solution containing a reducing agent for reduction. The reducing agent modifies the chemical structure of the precursor by transferring electrons and optimizing the electron cloud density. It also helps to remove residual impurities, further opening up some of the blocked initial channels, making the channel distribution more uniform. At the same time, it solidifies the layered stacked structure to prevent subsequent collapse. Finally, a triphenylphosphine-based conjugated hypercrosslinked polymer (PPh3-CHCP) with both layered stacked morphology and porous structure, high specific surface area and good chemical stability is obtained. The preparation process has controllable reaction conditions, is simple to operate, and the raw materials are readily available, which is conducive to large-scale production.

[0039] According to embodiments of this disclosure, the photochemically active monomer containing triphenylphosphine includes any one of triphenylphosphine and triphenylphosphine oxide, which is used as a crosslinking monomer for preparing PPh3-CHCP. It reacts with dimethoxybenzene to form carbon-carbon crosslinking bonds, constructing a three-dimensional network framework of the polymer precursor. The planar structure of the benzene ring of dimethoxybenzene is easily stacked to form a layered morphology, and it differs from the molecular structure of the photochemically active monomer containing triphenylphosphine, which allows initial pores to be naturally formed in the three-dimensional network. At the same time, it can also enhance the chemical stability of PPh3-CHCP, making it less prone to deformation during the depolymerization reaction at 80~160℃.

[0040] Lewis acid catalysts are anhydrous ferric chloride. Lewis acid catalysts can stably exert catalytic effects under inert gas protection, activate the reaction sites of photochemically active monomers containing triphenylphosphine and dimethoxybenzene, promote the rapid reaction between the two to form cross-linked bonds, help build a three-dimensional network structure, and avoid reaction obstruction or the generation of by-products.

[0041] The reducing agent includes any one of sodium borohydride, sodium chloride, calcium chloride, potassium chloride, sodium bromide, potassium bromide, lithium bromide, sodium iodide, lithium iodide, and potassium iodide.

[0042] According to another aspect of this disclosure, a method for chemically recovering polymethyl methacrylate polymers is provided, comprising: adding the above-mentioned composite catalyst and polymethyl methacrylate polymers to an organic solvent to obtain a mixed solution; deoxygenating the mixed solution; heating the deoxygenated mixed solution to 80~160°C in an oxygen-free environment to cause the polymethyl methacrylate polymers to undergo a depolymerization reaction; and recovering the methyl methacrylate monomers after separation and purification.

[0043] According to embodiments of this disclosure, in an organic solvent, a composite catalyst is mixed with a polymethyl methacrylate polymer. The mixed solution is then deoxygenated to prevent oxygen from interfering with the catalytic reaction process or causing product oxidation. During the heated reaction, ferric salts initiate homolytic cleavage of the polymethyl methacrylate polymer chemical bonds through single-electron transfer, generating carbon-centered free radicals that induce CC backbone breakage. Quaternary ammonium salt chelating agents form active complexes with ferric ions, regulating their electronic structure and reactivity, while also playing a phase transfer role to promote mass transfer. PPh3-CHCP serves as a carrier to immobilize and disperse the active components, and its electron-rich triphenylphosphine groups react with Fe... 3+ Electronic interactions are generated, further optimizing catalytic activity. The three factors work together to gradually depolymerize the polymer into methacrylate monomers.

[0044] The chemical recycling method disclosed herein allows for depolymerization temperatures of, for example, 80℃, 90℃, 100℃, 120℃, 140℃, and 160℃, which are lower than traditional high-temperature (above 160℃) depolymerization processes, resulting in lower energy consumption. The entire recycling process requires no complex equipment; the mixing, deoxygenation, heating reaction, and separation steps are simple and controllable. The prepared methacrylate monomers can be directly used in high-end applications, such as biomedical materials, aerospace coating preparation, and nanocomposite material modification, rather than being downgraded for use as a partial fossil fuel substitute or a cheap filler for composite materials. This achieves efficient resource recycling and has significant practical value in alleviating waste plastic pollution.

[0045] According to embodiments of this disclosure, the recovery method further includes: after the depolymerization reaction is completed, separating the triphenylphosphine-based conjugated hypercrosslinked polymer from the composite catalyst, and recovering the triphenylphosphine-based conjugated hypercrosslinked polymer after washing and drying.

[0046] After the depolymerization reaction, the solid-state porous nature of PPh3-CHCP allows for separation from the reaction system via simple filtration or centrifugation. The separated PPh3-CHCP is then washed and dried to recover the catalyst. The stable three-dimensional cross-linked structure of PPh3-CHCP prevents structural collapse during the depolymerization reaction (80–160 °C) and recovery process, maintaining good catalytic activity and structural stability after recovery. It can be recycled for subsequent depolymerization reactions, reducing catalyst loss, significantly decreasing costs, and improving the resource utilization and economic efficiency of the entire recovery process.

[0047] According to embodiments of this disclosure, the molar ratio of ferric salt to quaternary ammonium salt chelating agent is 1:0.01 to 1:100, for example, 1:0.1, 1:1, 1:5, 1:10, 1:20, 1:50, 1:100, etc. This ratio range ensures that the chelating agent effectively forms an active complex with ferric ions, regulates its electronic structure and reactivity, and at the same time plays a phase transfer role to promote mass transfer. It also synergistically enhances catalytic efficiency with triphenylphosphine-based conjugated hypercrosslinked polymers. The preferred molar ratio of ferric salt to quaternary ammonium salt chelating agent is 1:0.1 to 10.

[0048] The amount of triphenylphosphine-based conjugated hypercrosslinked polymer used is 1–10 mg / mL, for example, 1 mg / mL, 3 mg / mL, 5 mg / mL, 7 mg / mL, 10 mg / mL, etc. Appropriate dosage ensures sufficient immobilization and dispersion of the active components in the composite catalyst, utilizing its own electron-rich groups and Fe... 3+ The electronic interactions optimize catalytic activity while avoiding excessive dosage that could hinder mass transfer or waste costs.

[0049] According to embodiments of this disclosure, the molar ratio of polymethyl methacrylate polymer to ferric ions in the composite catalyst is 1:0.1 to 10, for example, 1:0.1, 1:1, 1:3, 1:5, 1:7, 1:10, etc. This ratio range ensures the catalytic activity of the composite catalyst, particularly the Fe content. 3+ To fully leverage catalytic activity, the homolytic cleavage of related chemical bonds in polymethacrylate polymer chains is initiated through single-electron transfer, generating carbon-centered radicals to induce CC backbone breakage. Simultaneously, the synergistic effect of quaternary ammonium salt chelating agents and PPh3-CHCP avoids the degradation caused by Fe... 3+ Insufficient dosage leads to low catalytic efficiency, while excessive dosage can cause resource waste or product contamination.

[0050] According to embodiments of this disclosure, the polymethacrylate polymer is any one of polymethyl methacrylate, polybutyl methacrylate, and benzyl methacrylate, and the concentration of the polymethacrylate polymer in the organic solvent is 50~2000mM. The chemical recovery method of this disclosure can achieve the depolymerization and recovery of various polymethacrylate polymers at different concentrations. This composite catalyst system exhibits good catalytic activity for various polymethacrylate polymers and has a wide substrate applicability range.

[0051] The organic solvent includes any one of acetonitrile, acetone, dichlorobenzene, dimethyl sulfoxide, N,N-dimethylformamide, n-butanol, and xylene. Acetonitrile is preferred because it has good solubility for polymethyl methacrylate polymers and composite catalyst components, ensuring uniform dispersion of the reaction system to improve depolymerization efficiency. It also replaces highly polluting chlorinated solvents, further enhancing the environmental friendliness of the entire recycling process.

[0052] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments. Unless otherwise specified, all methods described in the embodiments are conventional and can be performed according to the techniques or conditions described in the literature or the product manual.

[0053] Example 1

[0054] Example 1 of this disclosure provides a chemical recovery method for polybenzyl methacrylate (PBzMA), the specific process of which is as follows.

[0055] (1) Preparation of triphenylphosphine-based conjugated hypercrosslinked polymer (PPh3-CHCP)

[0056] 330 mg of triphenylphosphine, 1.6 g of dimethoxybenzene, and 5.8 g of anhydrous ferric chloride were weighed and added to a two-necked flask, followed by 20 mL of nitrobenzene solvent to form a mixed solution. The mixed solution was heated in an oil bath under a nitrogen atmosphere, and the reaction was carried out under reflux at 80 °C with stirring for 4 hours. The temperature was then increased to 120 °C and the reaction continued for 20 hours. After the reaction was complete, the solution in the flask was filtered, and the product was washed successively with methanol, tetrahydrofuran, and acetone until the filtrate was clear and transparent. The product was then subjected to Soxhlet extraction with methanol and tetrahydrofuran solutions for 24 hours, respectively. After extraction, the product was dried in a vacuum drying oven at 45 °C for 12 hours, and then ground to obtain a black powdery polymer precursor PPh3-HCP.

[0057] 560 mg of PPh3-HCP was weighed and placed in a 100 mL two-necked flask. 50 mL of methanol was added and the mixture was dispersed evenly. Then, 800 mg of sodium borohydride was added. The reaction system was heated to 80 °C and nitrogen gas was introduced. The reaction was allowed to proceed for 4 hours. After the reaction was completed, the solution was centrifuged. The separated product was washed three times each with 5 mol / L sodium hydroxide solution, deionized water, and methanol by centrifugation. After drying in a vacuum drying oven at 45 °C for 8 hours, triphenylphosphine-based conjugated hypercrosslinked polymer (PPh3-CHCP) was obtained.

[0058] Figure 1 This is a scanning electron microscope image of the triphenylphosphine-based conjugated hypercrosslinked polymer in Example 1.

[0059] like Figure 1 As shown, PPh3-CHCP exhibits a layered, stacked porous structure, with sodium ions from sodium borohydride embedded within the cross-linked framework. This layered stacked structure, along with its high specific surface area, lays the structural foundation for subsequent immobilization and dispersion of catalytically active components and enhances the accessibility of active sites. Simultaneously, the embedded alkali metal sodium ions further optimize the electronic environment of the PPh3-CHCP material, contributing to improved catalytic performance.

[0060] Figure 2 The image shows the UV-Vis absorption spectrum of the triphenylphosphine-based conjugated hypercrosslinked polymer in Example 1.

[0061] like Figure 2 As shown in the figure, PPh3-CHCP exhibits photosensitivity. Since its preparation raw material is a photochemically active monomer containing triphenylphosphine, the photochemical response characteristics of triphenylphosphine, as a photoactive functional group, are retained in the PPh3-CHCP framework. Simultaneously, its continuous conjugated cross-linked network broadens the light absorption range and enhances light absorption capacity, further strengthening photosensitivity. PPh3-CHCP exhibits a strong ultraviolet absorption peak in the 200 nm to 900 nm range, indicating a broad catalytic range.

[0062] (2) Chemical recovery of PBzMA

[0063] Weigh out 1.5 mg of PPh3-CHCP, 0.15 g of PBzMA (number average molecular weight of 12000, molecular weight distribution of 1.07), 0.04 g of tetrabutylammonium bromide (TBABr), 0.77 mL of acetonitrile (MeCN), and 25 μL of 10 mg / mL ferric chloride (FeCl3) solution in sequence, add them to a 10 mL sealed Shrek tube, and stir until all components are completely dispersed to obtain a mixed solution.

[0064] The mixed solution was deoxygenated through a three-cycle process of freezing-evacuation-inflation-evacuation-thawing. The deoxygenated mixed solution was then heated to 120°C and stirred for 2 hours in an oxygen-free environment to allow PBzMA to undergo depolymerization. After separation and purification, the benzyl methacrylate monomer was recovered.

[0065] Figure 3 The image shows the 1H NMR spectrum of the benzyl methacrylate monomer formed by depolymerization of polymethyl methacrylate in Example 1 of this disclosure via chemical recycling.

[0066] like Figure 3 As shown in the spectrum, two sharp singlets (c') are present at δ 5.55 ppm and δ 6.10 ppm, corresponding to 1H, respectively; one sharp singlet (b') is present at δ 5.10 ppm, corresponding to 2H; one sharp singlet (c) is present at δ 1.95 ppm, corresponding to 3H; and multiplets (a, a') are present near δ 7.35 ppm, corresponding to 5H. The chemical shifts and splitting modes of each characteristic peak are consistent with the standard spectrum of benzyl methacrylate monomer. Figure 1 To whom this disclosure is made: The chemical recovery method can successfully depolymerize PBzMA into the target monomer, and the depolymerization rate can reach 90% as verified by integral ratio analysis.

[0067] Example 2

[0068] Example 2 of this disclosure provides a chemical recovery method for polymethyl methacrylate (PMMA). The difference from Example 1 is that 0.15 g of PBzMA is replaced with 0.15 g of polymethyl methacrylate (number average molecular weight of 11,000 and molecular weight distribution of 1.08), so that PMMA undergoes a depolymerization reaction, and the methyl methacrylate monomer is recovered after separation and purification.

[0069] Figure 4 The above is a hydrogen nuclear magnetic resonance (NMR) spectrum of the methyl methacrylate monomer formed after depolymerization of polymethyl methacrylate by a chemical recycling method in Example 2.

[0070] like Figure 4 As shown in the spectrum, the monomer characteristic peak a' (δ 5.55, 6.10 ppm) can be observed, but very obvious broad, bag-shaped peaks (a, b) are observed in the δ 1.0-2.2 ppm range, consistent with the characteristic peak signals of the PMMA main chain. The monomer methyl singlet at δ 1.95 ppm is completely overlapped by the broad polymer peak. This indicates that the product is a mixture of monomer and incompletely depolymerized polymer.

[0071] Example 3

[0072] Example 3 of this disclosure provides a chemical recovery method for polybutyl methacrylate (PBMA). The difference from Example 1 is that 0.15 g of PB2MA is replaced with 0.15 g of PBMA (number average molecular weight of 11700 and molecular weight distribution of 1.15), so that PBMA undergoes a depolymerization reaction, and butyl methacrylate is recovered after separation and purification.

[0073] Figure 5 The 1H NMR spectrum of the butyl methacrylate monomer formed after depolymerization of polybutyl methacrylate by chemical recycling method in Example 3 is disclosed.

[0074] like Figure 5 As shown in the spectrum, the characteristic signals of the monomer butyl methacrylate (BMA) (olefin singlet at δ 6.10 and 5.55 ppm, and triplet at δ 4.05 ppm) can be observed. However, in the δ 0.8–2.5 ppm range, a broad peak signal appears, covering the expected signal regions of the monomer butyl chain (δ 0.95, 1.40, 1.65 ppm) and α-methyl (δ 1.95 ppm), causing the sharp peaks or coupling peak groups of these monomers to broaden. This broad peak is the characteristic peak signal of the polybutyl methacrylate backbone. The above phenomena indicate that the depolymerization reaction is incomplete, and the product is a mixture of BMA monomer and PBMA polymer.

[0075] Comparative Example 1

[0076] Comparative Example 1 of this disclosure provides a chemical recovery method for polybenzyl methacrylate, which differs from Example 1 in that the PPh3-CHCP used for depolymerization in the chemical recovery method is replaced with 1.5 mg of o-phenanthroline-based conjugated hypercrosslinked polymer (Phen-CHCP). The preparation method of Phen-CHCP is as follows.

[0077] 490 mg of 4,7-dimethyl-1,10-phenanthroline, 1.7 g of dimethoxybenzene, and 5.7 g of anhydrous ferric chloride were weighed and added to a two-necked flask, followed by 20 mL of nitrobenzene solvent to form a mixed solution. The mixed solution was heated in an oil bath under a nitrogen atmosphere, and the reaction was carried out at 80 °C with stirring under reflux for 8 hours. The reaction system was then heated to 120 °C and the reaction continued for 16 hours. After the reaction was completed, the solution in the flask was filtered, and the product was washed successively with methanol, tetrahydrofuran, and acetone until the filtrate was clear and transparent. The product was then subjected to Soxhlet extraction with methanol and tetrahydrofuran solutions for 24 hours, respectively. After extraction, the product was dried in a vacuum drying oven at 45 °C for 12 hours, and then ground to obtain a dark brown powdery polymer precursor, Phen-HCP.

[0078] Weigh 400 mg of Phen-HCP into a 100 mL two-necked flask, add 50 mL of methanol to disperse it evenly, then add 400 mg of hydrazine hydrate. Heat the reaction system to 75 °C and purge with nitrogen gas, react for 4 hours, then cool to room temperature and react for another 8 hours. After the reaction is complete, centrifuge the resulting solution, and wash the separated product three times each with 5 mol / L sodium hydroxide solution, deionized water, and methanol. Dry the product in a vacuum drying oven at 45 °C for 8 hours to obtain Phen-CHCP.

[0079] Comparative Example 2

[0080] Comparative Example 2 of this disclosure provides a chemical recovery method for polybenzyl methacrylate, which differs from Example 1 in that PPh3-CHCP is not added in the chemical recovery method.

[0081] The depolymerization rate of polymethacrylate polymers in Examples 1 to 3 and Comparative Examples 1 to 2 was tested, and the test data are shown in Table 1.

[0082] Table 1

[0083] Group Depolymerization rate (%) Example 1 90 Example 2 27 Example 3 13 Comparative Example 1 47 Comparative Example 2 61

[0084] As shown in Table 1, the depolymerization rate of polybenzyl methacrylate in Example 1 reached 90%, significantly higher than that of Comparative Example 1 (47%) and Comparative Example 2 (61%), indicating that the PPh3-CHCP used has excellent catalytic effect on the depolymerization of this polymer. In Comparative Example 1, the depolymerization rate decreased significantly after replacing the catalyst with Phen-CHCP, and was lower than that of Comparative Example 2 without catalyst, indicating that Phen-CHCP has no obvious catalytic activity or even an inhibitory effect in this system. Therefore, the chemical recovery method for polybenzyl methacrylate disclosed in this paper, using a catalyst including PPh3-CHCP, tetrabutylammonium bromide, and ferric chloride, can achieve efficient chemical recovery of polymethyl methacrylate polymers.

[0085] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A composite catalyst for the chemical recovery of polymethacrylate polymers, characterized in that, The composite catalyst comprises a trivalent iron salt, a quaternary ammonium salt chelating agent, and a layered porous triphenylphosphine-based conjugated hypercrosslinked polymer, wherein... The triphenylphosphine-based conjugated hypercrosslinked polymer is prepared by a Friedel-Crafts alkylation reaction of a triphenylphosphine-containing photochemically active monomer and dimethoxybenzene under the catalysis of a Lewis acid catalyst.

2. The composite catalyst according to claim 1, characterized in that, The trivalent ferric salt includes any one of ferric chloride, sodium tetrachloroferrate, and ammonium tetrachloroferrate. The chelating agent includes either tetrabutylammonium bromide or tetrabutylammonium chloride.

3. The composite catalyst according to claim 1, characterized in that, The triphenylphosphine-based conjugated hypercrosslinked polymer has a particle size of 40-60 μm and a pore size of 1-3 nm.

4. The composite catalyst according to claim 1, characterized in that, The preparation method of the triphenylphosphine-based conjugated hypercrosslinked polymer includes: The triphenyl-containing photochemically active monomer and dimethoxybenzene are dissolved in an organic solvent in the Lewis acid catalyst to form a mixed solution; Friedel-Crafts alkylation reaction was carried out under inert gas protection and at a temperature of 80~140℃ to obtain the polymer precursor; Under a nitrogen atmosphere, the polymer precursor is dispersed in a solution containing a reducing agent for reduction treatment to obtain the triphenylphosphine-based conjugated hypercrosslinked polymer.

5. The composite catalyst according to any one of claims 1 to 4, characterized in that, The triphenyl-containing photochemically active monomer includes any one of triphenylphosphine and triphenylphosphine oxide; The Lewis acid catalyst is anhydrous ferric chloride; The reducing agent includes any one of sodium borohydride, sodium triacetoxyborohydride, sodium chloride, calcium chloride, potassium chloride, sodium bromide, potassium bromide, lithium bromide, sodium iodide, lithium iodide, and potassium iodide.

6. A method for the chemical recovery of polymethacrylate polymers, characterized in that, The recycling method includes: Add the composite catalyst described in any one of claims 1 to 5 and the polymethyl methacrylate polymer to an organic solvent to obtain a mixed solution; The mixed solution is subjected to deoxygenation treatment. The deoxygenated mixed solution is heated to 80~160℃ in an oxygen-free environment to cause the polymethacrylate polymer to undergo a depolymerization reaction. The methacrylate monomer is then recovered after separation and purification.

7. The chemical recovery method according to claim 6, characterized in that, The molar ratio of the trivalent iron salt to the quaternary ammonium salt chelating agent is 1:0.01 to 1:100, preferably 1:0.1 to 10; The amount of the triphenylphosphine-based conjugated hypercrosslinked polymer used is 1~10 mg / mL.

8. The chemical recovery method according to claim 6, characterized in that, The molar ratio of the polymethacrylate polymer to the ferric ions in the composite catalyst is 1:0.1~10.

9. The chemical recovery method according to claim 6, characterized in that, The polymethacrylate polymer is any one of polymethyl methacrylate, polybutyl methacrylate, and benzyl methacrylate; The concentration of the polymethacrylate polymer in the organic solvent is 50~2000 mM; The organic solvent includes any one of acetonitrile, acetone, dichlorobenzene, dimethyl sulfoxide, N,N-dimethylformamide, n-butanol, and xylene.

10. The chemical recovery method according to any one of claims 6 to 9, characterized in that, The recovery method further includes: after the depolymerization reaction is completed, separating the triphenylphosphine-based conjugated hypercrosslinked polymer from the composite catalyst, and washing and drying the triphenylphosphine-based conjugated hypercrosslinked polymer for recovery.

Images