Depolymerizable copolymer

Abstract

A depolymerizable copolymer according to the present disclosure is obtained by copolymerizing a first monomer that constitutes a depolymerizable homopolymer that decomposes into monomers by heating, light, or the like, and a second monomer that is different from the first monomer. The first monomer is alpha-methylstyrene (AMS) and the second monomer is butyl methacrylate (BMA). Such a depolymerizable copolymer has depolymerizability to decompose the polymer into monomers by heat or light and can be reused easily. The depolymerizable copolymer preferably has an AMS:BMA 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). The thermal decomposition temperature of the depolymerizable copolymer may be 190-370℃.

Description

Depolymerizable copolymer

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

[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, composite materials made from metal and plastic are currently disposed of in landfills because it is difficult to separate and recover the individual materials.

[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 recover and reuse plastics.

[0004] However, the environmental safety of biodegradable polymers during biodegradation, and the impact of the decomposition of bioplastics on environmental and marine organisms when they are ingested 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 need for materials and methods that can decompose plastics into monomers using simple methods such as heat or light and reuse them. For example, technologies have been studied for decomposing homopolymers such as polymethyl methacrylate and polystyrene into monomers using simple methods such as heat or light (e.g., Patent Document 1, Patent Document 2, and Non-Patent Document 1).

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

[0008] U.S. Patent No. 9,650,313 Patent Publication No. 2006-526582

[0009] Hajime Otani et al., "Thermal Decomposition Characteristics of Polymers," Polymers, Society of Polymer Science, 46-6, 394 (1997)

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

[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 butyl methacrylate (BMA) (Invention 1).

[0012] According to this invention (Invention 1), it has been discovered that copolymerizing butyl methacrylate (BMA) with α-methylstyrene (AMS), which constitutes a homopolymer with high depolymerizability, can produce a highly convenient depolymerizable copolymer that is easy to recycle and leaves little residue upon heating. While depolymerizable homopolymers have been known, the characteristics of polymers obtained by copolymerizing the monomer that constitutes the depolymerizable homopolymer with other monomers have not been clear. Therefore, the present inventors conducted extensive research into polymers obtained by copolymerizing the monomer that constitutes the depolymerizable homopolymer with other monomers, and as a result, they 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 butyl 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 depolymerizable copolymer that is depolymerizable, leaves no residue due to thermal decomposition, and allows complete recovery of constituent monomers by thermal decomposition, making it more convenient.

[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 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 190 to 370° 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.

[0019] The depolymerizable copolymer of the present invention is a copolymer of α-methylstyrene (AMS) as a first monomer and butyl methacrylate (BMA) as a second monomer that constitute a depolymerizable homopolymer that decomposes into monomers by heating, light, or the like, and is easy to recycle because the monomers can be recovered in high yield by a simple method using heating. Furthermore, because there is little residue after thermal decomposition, even when this polymer is combined with different materials such as metals to form composite materials, the polymer can be decomposed by simply heating and the monomers can be recovered, allowing for the separate recovery of the materials.

[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. Known examples of depolymerizable homopolymers with such high monomer recovery rates include polymethyl methacrylate (PMMA), poly-α-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, butyl methacrylate (BMA) is used as the second monomer to be copolymerized with α-methylstyrene (AMS).

[0023] (Characteristics of Depolymerizable Copolymer) The depolymerizable copolymer of the present invention is not particularly limited as long as it is a polymer in which α-methylstyrene (AMS) and butyl methacrylate (BMA) are copolymerized, but a copolymer in which the AMS:BMA 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 190 to 370°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 for Producing Depolymerizable Copolymer) The method for producing the depolymerizable copolymer is not particularly limited, and may be, for example, copolymerized by a 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 copolymer.

[0028] The depolymerizable copolymer of the present invention has been described above. However, the present invention is 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 butyl methacrylate (BMA). 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 a metal, which has traditionally been difficult to recycle, and therefore has extremely great industrial applicability.

[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 (90% solids, manufactured by Kao Corporation) were placed in a 2-L four-neck flask and dissolved with stirring. (2) After dissolution, α-methylstyrene (AMS) and butyl methacrylate (BMA) were added, and the system was purged with argon while stirring at 150 rpm (stirring blade: 10.5 cm wide, half-moon-shaped). (3) After confirming that the temperature inside the flask had reached 3-4°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 70 hours while maintaining the internal temperature at 3-4°C. (4) After 70 hours, a portion was sampled and added dropwise to methanol. A white solid precipitated, and it was determined that the reaction was proceeding. 2,6-di-tert-butyl-4-methylphenol was added to terminate the reaction. (5) The reaction solution was added dropwise to 3.75 L of methanol, and the precipitated white solid was recovered by centrifugation (9000 rpm for 10 minutes). (6) The supernatant was removed, and methanol was added for washing. (7) The mixture was then centrifuged at 9000 rpm for 10 minutes to recover the solid. (8) The resulting white solid was briefly dried and then dissolved in tetrahydrofuran (THF) (polymer concentration: 10 wt%). (9) The solution from (8) was added dropwise to 5.6 L of methanol, and the precipitated white solid was recovered by centrifugation (9000 rpm for 10 minutes). (10) The supernatant of this separated and recovered product was removed, and methanol 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 20 hours to obtain the final sample (yield: 20.2 g).

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

[0032]

[0033] [Example 2] (NMR, GPC, and TG-DTA Analysis of Depolymerizable Copolymer) The monomer ratio of the copolymer obtained in Example 1 was analyzed by NMR, and it was found to be AMS:BMA = 60:40 (molar ratio). Furthermore, the molecular weight of this copolymer was analyzed by GPC, and it was found to be number average molecular weight (Mn): 16,188, weight average molecular weight (Mw): 49,210, and molecular weight distribution (Mw / Mn): 3.0. Furthermore, the obtained copolymer was analyzed (N) using a thermogravimetric differential thermal analyzer (TG-DTA) capable of image observation. ２ When the temperature was increased in a 10°C / min environment (heating rate: 10°C / min), the decomposition onset temperature was approximately 190°C, the 50% decomposition temperature was approximately 320°C, and the decomposition completion temperature was approximately 370°C. With continued heating, ordinary polymers gradually decompose from the ends of the polymer molecules, causing discoloration and ultimately leaving behind a black residue. However, the copolymer of Example 1 did not show such discoloration due to decomposition, and it was confirmed that it completely decomposed into monomers, confirming its high depolymerization properties. The TG-DTA analysis results for the copolymer of Example 1 (P(AMS-BMA)) are shown in Table 2.

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

[0035]

[0036] As is clear from Table 1, 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) TG-DTA analysis of the copolymer synthesized in Example 1 (N ２The mixture was heated to 350° C. in a humid atmosphere (heating rate: 10° C. / min) and then maintained at 350° C. As a result, it was confirmed that decomposition was complete within 30 minutes of maintaining the temperature, and no residue was left.

[0038] Example 4 (TG-DTA / MS Analysis of Depolymerizable Copolymer) The copolymer of AMS and BMA obtained in Example 1 was subjected to mass spectrometry (TG-DTA / MS) of pyrolysis gas up to 500°C under the following conditions. As a result, AMS and BMA 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]

[0040]

[0041]

[0042] Example 5 (Thermal decomposition of depolymerizable copolymer, recovery of monomer, and recycling synthesis) The copolymer of AMS and BMA obtained in Example 1 was heated to 350°C at a rate of 10°C / min in 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, and a copolymer of AMS and BMA was obtained in the same manner 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 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 butyl methacrylate (BMA).

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

10.

3. 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.

4. The depolymerizable copolymer according to any one of claims 1 to 3, wherein the thermal decomposition temperature of the depolymerizable copolymer is 190 to 370°C.

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