Depolymerizable copolymer

Abstract

To provide a copolymer having depolymerization properties in which a polymer is decomposed into a monomer by heat or light, and enabling easy reuse.SOLUTION: A depolymerizable copolymer according to the present disclosure is obtained by copolymerizing a first monomer that constitutes a depolymerizable homopolymer decomposed into a monomer by heating, light, or the like, and a second monomer that is different from the first monomer. The first monomer is α-methylstyrene (AMS) and the second monomer is ethyl methacrylate (EMA). The depolymerizable copolymer preferably has an AMS:EMA of 90:10 to 10:90 (molar ratio). The weight-average molecular weight (Mw) of the depolymerizable copolymer may be 5,000-1,000,000 (Mw). Moreover, the thermal decomposition temperature of the depolymerizable copolymer may be 180-380°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a copolymer having depolymerizability in which a polymer is decomposed into monomers by heat or light, and particularly to a copolymer having depolymerizability that leaves little residue when depolymerized by heat. [Background technology]

[0002] Technological development of plastics (polymers) has progressed as materials with excellent durability and heat resistance, and a variety of materials are used on the market. However, these plastic materials do not naturally decompose in the environment. For this reason, their impact on the environment has been pointed out, but at present, sufficient recycling technology has not been established, and many of them are discarded. In particular, in the case of composite materials that combine metal and plastic, it is difficult to separate and recover the individual materials, so most of them are currently disposed of in landfills.

[0003] In recent years, in response to growing interest in the SDGs, various efforts have been made to develop technologies for decomposing plastics, such as biodegradable polymers, and to collect and reuse plastics.

[0004] However, the environmental safety of biodegradable polymers during biodegradation, as well as the impact of the decomposition of bioplastics into microplastics and their subsequent ingestion by environmental and marine organisms, remain unclear. Furthermore, while biodegradable polymers are effective in reducing waste to a certain extent, they have not yet achieved a fundamental solution to the issue of reuse, due to issues such as the poor physical properties of recycled products. Furthermore, from the perspective of waste reduction, they also pose a problem in that they take a long time to decompose, sometimes taking several months or more.

[0005] In addition, PET bottles and other items are recycled and reused, but in conventional mechanical recycling, they become discolored with repeated use, so a certain amount of virgin polymer needs to be added. Furthermore, chemical recycling requires the use of special chemicals to break them down into monomers, which requires a great deal of effort and energy. Another problem is that the uses of recycled products are limited.

[0006] Therefore, there is a demand for materials and methods that can decompose plastics into monomers using simple methods such as heat or light, and then reuse them.For example, technologies have been studied that can decompose homopolymers such as polymethyl methacrylate and polystyrene into monomers using simple methods such as heat or light (for example, Patent Document 1, Patent Document 2, Non-Patent Document 1).

[0007] However, even in this case, it is desirable to be able to perform pyrolysis at a lower temperature. Furthermore, for polystyrene, the monomer recovery rate during pyrolysis is low at 60 to 70%, so it is desirable to increase the monomer recovery rate (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 9,650,313 [Patent Document 2] Special Publication No. 2006-526582 [Non-patent literature]

[0009] [Non-Patent Document 1] Hajime Otani et al., "Thermal Decomposition Characteristics of Polymers," Polymer, Society of Polymer Science, 46-6, 394 (1997) Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in view of the above-mentioned problems, and aims to provide a copolymer that has depolymerizability, i.e., the polymer is decomposed into monomers by heat or light, and that can be easily reused. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides a depolymerizable copolymer obtained by copolymerizing a first monomer constituting a depolymerizable homopolymer that decomposes into monomers by heating, light, or the like with a second monomer different from the first monomer, wherein the first monomer is α-methylstyrene (AMS) and the second monomer is ethyl methacrylate (EMA) (Invention 1).

[0012] According to this invention (Invention 1), it has been discovered that copolymerizing α-methylstyrene (AMS), which constitutes a homopolymer with high depolymerizability, with ethyl methacrylate (EMA) can produce a highly convenient depolymerizable copolymer that is easy to recycle and leaves little residue when heated. While depolymerizable homopolymers have been known, the properties of polymers obtained by copolymerizing the monomers that constitute the depolymerizable homopolymer with other monomers have not been clear. Therefore, the inventors of the present invention conducted extensive research into polymers obtained by copolymerizing the monomers that constitute the depolymerizable homopolymer with other monomers, and have confirmed that the copolymer described in Invention 1 is a polymer that is depolymerizable, leaves no residue upon thermal decomposition, and allows the constituent monomers to be completely recovered by thermal decomposition.

[0013] In the above invention (Invention 1), the molar ratio of α-methylstyrene to ethyl methacrylate in the depolymerizable copolymer is preferably 10:90 to 90:10 (Invention 2).

[0014] According to this invention (Invention 2), it is possible to obtain a more convenient depolymerizable copolymer that has depolymerizability, leaves no residue upon thermal decomposition, and allows complete recovery of the constituent monomers upon thermal decomposition.

[0015] In the above invention (Invention 1), the weight average molecular weight (Mw) of the depolymerizable copolymer is preferably 5,000 to 1,000,000 (Invention 3).

[0016] According to this invention (Invention 3), it is possible to obtain a highly convenient depolymerizable copolymer that has depolymerizability, leaves no residue upon thermal decomposition, and allows complete recovery of the constituent monomers upon thermal decomposition.

[0017] Furthermore, in the above inventions (Inventions 1 to 3), the thermal decomposition temperature of the depolymerizable copolymer is preferably 180 to 380° C. (Invention 4).

[0018] According to this invention (Invention 4), a depolymerizable copolymer can be obtained which has depolymerizability, leaves no residue due to thermal decomposition, allows complete recovery of constituent monomers by thermal decomposition, is highly convenient, and has excellent recoverability, particularly at low temperatures. [Effects of the Invention]

[0019] The depolymerizable copolymer of the present invention is a copolymer of α-methylstyrene (AMS) as the first monomer and ethyl methacrylate (EMA) as the second monomer, which constitute a depolymerizable homopolymer that decomposes into monomers by heating or light. The monomers can be recovered in high yields by a simple method using heat, making it easy to recycle. Furthermore, because the residue after thermal decomposition is small, even when this polymer is combined with different materials such as metals to form composite materials, the polymer can be decomposed by simply heating to recover the monomers, allowing for the separate recovery of the materials. DETAILED DESCRIPTION OF THE INVENTION

[0020] The depolymerizable copolymer of the present invention will be described in detail below.

[0021] (Depolymerizable Homopolymer and First Monomer) The depolymerizable homopolymer in the present invention is obtained by polymerizing a specific monomer alone, and is preferably one that can be decomposed into monomers by heating, light, or the like, and has an extremely high monomer recovery rate of 90% or more. Examples of depolymerizable homopolymers with such high monomer recovery rates include polymethyl methacrylate (PMMA), polyα-methylstyrene (PAMS), and polytetrafluoroethylene (PTFE). The monomers (monomer components) that constitute these homopolymers are methyl methacrylate (MMA), α-methylstyrene (AMS), and tetrafluoroethylene (TFE). In the present invention, α-methylstyrene (AMS) is used as the first monomer that constitutes the depolymerizable homopolymer, which is the raw material.

[0022] (Second Monomer) In the depolymerizable copolymer of the present invention, ethyl methacrylate (EMA) is used as the second monomer to be copolymerized with α-methylstyrene (AMS).

[0023] (Characteristics of depolymerizable copolymers) The depolymerizable copolymer of the present invention is not particularly limited as long as it is a polymer in which α-methylstyrene (AMS) and ethyl methacrylate (EMA) are copolymerized, but a copolymer in which the AMS:EMA ratio is 10:90 to 90:10 (molar ratio), particularly 20:80 to 80:20 (molar ratio), and further particularly 30:70 to 70:30 (molar ratio) is preferred.

[0024] The weight average molecular weight (Mw) of the depolymerizable copolymer of the present invention is not particularly limited, but is preferably 5,000 to 1,000,000 (Mw), and more preferably 10,000 to 500,000 (Mw).

[0025] Furthermore, the thermal decomposition temperature of the depolymerizable copolymer of the present invention is not particularly limited as long as it is a temperature at which thermal decomposition can be achieved, but is preferably 180 to 380°C, and particularly preferably 250 to 350°C.

[0026] The depolymerizable copolymer may contain any suitable additives as needed, such as crosslinkers, tackifiers, plasticizers (e.g., trimellitic ester plasticizers, pyromellitic ester plasticizers, etc.), pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, UV absorbers, light stabilizers, release agents, softeners, surfactants, flame retardants, and antioxidants.

[0027] (Method of producing depolymerizable copolymer) The method for producing the depolymerizable copolymer is not particularly limited, and may be, for example, copolymerization by radical polymerization reaction. Specifically, the depolymerizable copolymer can be produced by sealing raw material monomers together with a solvent containing a radical polymerization initiator, a crosslinking agent, etc. under an inert gas atmosphere, continuously stirring for a long period of time to copolymerize the monomers, and then precipitating the copolymer in a poor solvent and recovering the precipitate.

[0028] The depolymerizable copolymer of the present invention has been described above. The present invention relates to a depolymerizable copolymer obtained by copolymerizing a first monomer constituting a depolymerizable homopolymer that decomposes into monomers by heating, light, or the like with a second monomer different from the first monomer, where the first monomer is α-methylstyrene (AMS) and the second monomer is ethyl methacrylate (EMA). Such a depolymerizable copolymer has excellent recyclability because the monomer can be easily recovered by heating even when molded with a different material such as metal, which has traditionally been difficult to recycle, and its industrial applicability is extremely great. [Example]

[0029] The present invention will be described in more detail based on the following specific examples, but the present invention is not limited to the following examples.

[0030] [Example 1] (Synthesis of depolymerizable copolymer) (1) Ion-exchanged water, sodium carbonate, and KS soap (solid content 90%, manufactured by Kao Corporation) were placed in a 2 L four-neck flask and dissolved with stirring. (2) After dissolution, α-methylstyrene (AMS) and ethyl methacrylate (EMA) were added, and the system was purged with argon while stirring at 150 rpm (stirring blade: 10.5 cm wide, half-moon type). (3) After confirming that the temperature inside the flask had reached 3 to 4°C, sodium dithionite, sodium ferric ethylenediaminetetraacetate trihydrate, tetrasodium ethylenediaminetetraacetate tetrahydrate, sodium formaldehyde sulfoxylate, and cumene hydroperoxide (80%) were added in that order, and the mixture was stirred for 67 hours while maintaining the internal temperature at 3 to 4°C. (4) After 67 hours, a portion was sampled and added dropwise to methanol. A white solid precipitated, and it was determined that the reaction was progressing. 2,6-di-tert-butyl-4-methylphenol was added to stop the reaction. (5) The reaction solution was added dropwise to 3.75 L of methanol, and the precipitated white solid was collected by centrifugation (9000 rpm for 10 minutes). (6) The supernatant was removed, and MeOH was added for washing. (7) Then, the mixture was centrifuged at 9000 rpm for 10 minutes to collect the solid. (8) The obtained white solid was simply dried and then dissolved in tetrahydrofuran (THF) (polymer concentration: 10 wt %). (9) The solution of "(8)" was added dropwise to 500 mL of methanol, and the precipitated white solid was collected by centrifugation (9000 rpm for 10 minutes). (10) The supernatant of this separated and recovered product was removed, and MeOH was added for washing. (11) Then, the mixture was centrifuged at 9000 rpm for 10 minutes to collect the solid. (12) The resulting white solid was dried under reduced pressure at 50°C for 24 hours to obtain the final sample (yield: 3.22 g).

[0031] The amounts of each raw material used in the above synthesis method are shown in Table 1 below.

[0032] [Table 1]

[0033] [Example 2] (NMR, GPC, and TG-DTA analysis of depolymerizable copolymers) The monomer ratio of the copolymer obtained in Example 1 was analyzed by NMR, and the AMS:EMA ratio was 58:42 (molar ratio). Furthermore, the molecular weight of this copolymer was analyzed by GPC, and the number average molecular weight (Mn): 8,040, weight average molecular weight (Mw): 30,676, and molecular weight distribution (Mw / Mn): 3.8. Furthermore, when the obtained copolymer was analyzed using a thermogravimetric differential thermal analyzer (TG-DTA) capable of image observation (N environment, heating rate 10°C / min), the decomposition onset temperature was approximately 180°C, the 50% decomposition temperature was approximately 340°C, and the decomposition end temperature was approximately 380°C. When conventional polymers are continuously heated, they gradually decompose from the ends of the polymer molecules, causing discoloration and ultimately leaving a black residue. However, the copolymer of Example 1 did not show such decomposition-related discoloration, and complete decomposition into monomers was observed, confirming its high depolymerization ability. The TG-DTA analysis results of the copolymer (P(AMS-EMA)) of Example 1 are shown in Table 2.

[0034] [Comparative Example 1] (TG-DTA analysis of polycarbonate) As an example of a polymer with low depolymerizability, TG-DTA analysis (N2 environment, heating rate 10°C / min) of polycarbonate (PC) showed that the decomposition temperature started at about 400°C, the material gradually turned black, the temperature at which 50% decomposition ended was about 520°C, and decomposition proceeded to about 70%, but about 30% remained undecomposed as a residue. The TG-DTA analysis results for this polycarbonate are also shown in Table 2.

[0035] [Table 2]

[0036] As is clear from Table 2, it was found that the copolymer obtained in Example 1 can be completely decomposed at a temperature lower than that of polycarbonate (PC).

[0037] [Example 3] (TG-DTA analysis of depolymerizable copolymer) In TG-DTA analysis (N environment, heating rate 10°C / min) of the copolymer synthesized in Example 1, the temperature was maintained at 350°C after heating to 350°C. As a result, it was confirmed that decomposition was completed within 30 minutes of maintaining the temperature, and no residue was left.

[0038] [Example 4] (TG-DTA / MS analysis of depolymerizable copolymers) Mass spectrometry (TG-DTA / MS) of the pyrolysis gas of the copolymer of AMS and EMA obtained in Example 1 was performed up to 500°C under the following conditions. As a result, AMS and EMA were detected as components generated by pyrolysis, but no other components were detected. The TG-DTA / MS analysis conditions are shown in Tables 3 to 5.

[0039] [Table 3]

[0040] [Table 4]

[0041] [Table 5]

[0042] [Example 5] (Thermal decomposition of depolymerizable copolymers, recovery of monomers, and recycling synthesis) The copolymer of AMS and EMA obtained in Example 1 was heated to 350°C at a rate of 10°C / min under an argon flow environment, maintained at 350°C, and the vaporized component was cooled to room temperature to obtain a liquid component. This liquid component was subjected to polymer synthesis in the same manner as in Example 1, resulting in a copolymer of AMS and EMA, as in Example 1, confirming that the copolymer can be reused repeatedly.

Claims

1. A depolymerizable copolymer obtained by copolymerizing a first monomer constituting a depolymerizable homopolymer that is decomposed into monomers by heating, light, or the like, and a second monomer different from the first monomer, the first monomer is alpha-methylstyrene (AMS) and the second monomer is ethyl methacrylate (EMA); The depolymerizable copolymer has a decomposition starting temperature of 180°C and a decomposition ending temperature of 380°C when analyzed (in a N 2 environment, at a temperature increase rate of 10°C / min) using a thermogravimetric differential thermal analyzer (TG-DTA) capable of image observation.

2. 2. The depolymerizable copolymer according to claim 1, wherein the molar ratio of α-methylstyrene to ethyl methacrylate in the depolymerizable copolymer is 10:90 to 90:

10.

3. 2. The depolymerizable copolymer according to claim 1, wherein the weight average molecular weight (Mw) of the depolymerizable copolymer is 5,000 to 1,000,000.

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