Depolymerizable copolymer

Abstract

A depolymerizable copolymer according to the present disclosure is obtained by copolymerizing a first monomer which constitutes a depolymerizable homopolymer capable of being decomposed into a monomer by heating, light, or the like, and a second monomer which is different from the first monomer, wherein the first monomer is methyl methacrylate (MMA) and the second monomer is styrene (St). The depolymerizable copolymer has depolymerization properties such that a polymeric substance (a polymer) is decomposed into a monomeric substance (a monomer) by heat or light, and can be easily reused. It is preferable that the depolymerizable copolymer has an MMA:St ratio (molar ratio) of 90:10 to 10:90. The weight average molecular weight (Mw) of the depolymerizable copolymer may be 5,000 to 1,000,000 (Mw). In addition, the thermal decomposition temperature of the depolymerizable copolymer may be 280°C to 500°C.

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, 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 Documents 1 and 2).

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

[0009] Hajime Otani et al., "Thermal Decomposition Characteristics of Polymers," Polymer, Society of Polymer Science, 46-6, 394 (1997); Tadashi Arii, "Thermal Decomposition of Polystyrene by Simultaneous Differential Thermogravimetry-Mass Spectrometry (TG-MS)," J. Mass Spectron. Soc. Jpn., Vol. 51, No. 1, 235 (2003)

[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 methyl methacrylate (MMA) and the second monomer is styrene (St) (Invention 1).

[0012] According to this invention (Invention 1), it has been discovered that copolymerizing methyl methacrylate (MMA), which constitutes a homopolymer with high depolymerizability, with styrene (St) 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 properties of polymers obtained by copolymerizing the monomer that constitutes the depolymerizable homopolymer with other monomers have not been elucidated. Therefore, the present inventors conducted extensive research into polymers obtained by copolymerizing the monomer that constitutes 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 methyl methacrylate to styrene 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 280 to 500° 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, and is highly convenient and easy to handle.

[0019] The depolymerizable copolymer of the present invention is a copolymer of methyl methacrylate (MMA) as a first monomer and styrene (St) as a second monomer that constitute a depolymerizable homopolymer that decomposes into monomers by heating, light, etc., 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 separation and 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, methyl methacrylate (MMA) 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, styrene (St) is used as the second monomer to be copolymerized with methyl methacrylate (MMA).

[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 methyl methacrylate (MMA) and styrene (St) are copolymerized, but a copolymer in which MMA:St is composed of 90:10 to 10:90 (molar ratio), particularly 90:10 to 20:80 (molar ratio), and further 90:10 to 30:70 (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 280 to 500°C, and more preferably 290 to 450°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 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, wherein the first monomer is methyl methacrylate (MMA) and the second monomer is styrene (St). The depolymerizable copolymer of the present invention 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) Styrene (St; 25.00 g), methyl methacrylate (MMA; 24.03 g), toluene (173.38 g), and azobisisobutyronitrile (AIBN) (0.490 g) were placed in a 500 ml four-neck flask and dissolved with stirring. (2) After dissolution, the flask was cooled with ice water and degassed by repeatedly reducing the pressure and leaking Ar 10 times. (3) After degassing, the flask was sealed and polymerization was carried out in an oil bath at 80°C for 20 hours. (4) After confirming the reaction rate (approximately 60%) by 1H-NMR, the reaction solution was added dropwise to methanol (2.8 L) for reprecipitation. (5) The polymer was recovered by suction filtration. (6) The recovered polymer was dried under reduced pressure at 50°C for 10 hours. (7) After drying under reduced pressure, the polymer was dissolved in THF (263.6 g) and then added dropwise to methanol (3.7 L) to cause reprecipitation. (8) The polymer was recovered by suction filtration. (9) The recovered polymer was dried under reduced pressure at 50°C for 18 hours. (10) The dried polymer was recovered to obtain the final product (26.3 g).

[0031] [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 MMA:St = 47:53 (molar ratio). Furthermore, the molecular weight of this copolymer was analyzed by GPC, and it was found to be number average molecular weight (Mn): 16,134, weight average molecular weight (Mw): 29,943, and molecular weight distribution (Mw / Mn): 1.86. 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 290°C, the 50% decomposition temperature was approximately 390°C, and the decomposition completion temperature was approximately 430°C. With continued heating, a typical polymer gradually decomposes 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 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(St-MMA)) are shown in Table 1.

[0032] Comparative Example 1 (TG-DTA Analysis of Polycarbonate) As an example of a polymer with low depolymerization property, TG-DTA analysis of polycarbonate (N ２ As a result of the test (heating rate 10°C / min) the decomposition started at about 400°C, the material gradually turned black, and the decomposition ended at about 550°C. The decomposition proceeded to about 70%, but about 30% remained undecomposed as a residue.

[0033] Comparative Example 2 (TG-DTA Analysis of Polystyrene) TG-DTA analysis (N ２ As a result of the heating (heating rate of 10°C / min) the decomposition starting temperature was about 360°C, the 50% decomposition temperature was about 410°C, and the decomposition completion temperature was about 440°C. No residue was left after heating. The TG-DTA analysis results of this polystyrene (PSt) are also shown in Table 1.

[0034]

[0035] As is clear from Table 1, it was found that the poly(styrene-methyl methacrylate) of Example 1 can be decomposed at a lower temperature than polystyrene, which is the polymer of the second monomer component.

[0036] [Example 3] (TG-DTA analysis of depolymerizable copolymer) TG-DTA analysis of the copolymer synthesized in Example 1 (N ２ In a test environment (temperature rise rate: 10°C / min), the copolymer of Example 1 was heated to 400°C and then maintained at 400°C. As a result, it was confirmed that the decomposition was completed within 30 minutes of maintaining the temperature, and no residue was left. In other words, it was found that the copolymer of Example 1 could be completely decomposed by heating and maintaining the temperature at 400°C.

[0037] [Example 4] (TG-DTA / MS analysis of depolymerizable copolymer) The copolymer of St and MMA obtained in Example 1 was subjected to mass analysis (TG-DTA / GC-MS) of the pyrolysis gas under the conditions shown in Tables 2 to 4. As a result, St and MMA were detected as components generated by pyrolysis, and no other components were detected.

[0038]

[0039]

[0040]

[0041] Comparative Example 3 (TG-DTA / MS Analysis of Polystyrene) When the pyrolysis gas of polystyrene was subjected to mass spectrometry (TG-DTA / GC-MS) in the same manner as in Example 2, it was reported that 70% of the polystyrene was detected as a monomer, but the remainder consisted of styrene dimers and trimers, and it was not possible to completely recover the styrene.

[0042] In contrast, the copolymer of Example 1 can be decomposed at a lower temperature than polystyrene, as shown in the results of Comparative Example 2 and Example 4, and it was found that the styrene and methyl methacrylate monomers could be completely recovered.

[0043] [Example 5] (Recovery of thermodecomposed monomers from depolymerizable copolymers, and recycling synthesis) The copolymer of St and MMA obtained in Example 1 was heated to 400°C at a heating rate of 10°C / min in an argon flow environment, 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 as a result, a copolymer of St and MMA similar to that in Example 1 was obtained, confirming that it can be reused repeatedly.

[0044] Example 6 (Synthesis of Depolymerizable Copolymer, Monomer Recovery by Thermal Decomposition, and Recycling Synthesis) 1) Synthesis of Depolymerizable Copolymer (1) Styrene (St; 25.00 g), methyl methacrylate (MMA; 24.03 g), THF (173.38 g), and AIBN (0.490 g) were charged into a 500 ml four-neck flask and dissolved with stirring. (2) After dissolution, the flask was cooled with ice water and degassed by repeatedly reducing the pressure and leaking Ar 10 times. (3) After degassing, the flask was sealed, and polymerization was carried out at an internal temperature of 65°C for 48 hours. (4) After confirming the reaction rate by 1H-NMR (approximately 70%), the reaction solution was added dropwise to methanol (2.8 L) and reprecipitated. (5) The polymer was recovered by suction filtration. (6) The recovered polymer was dried under reduced pressure at 50°C for 10 hours. (7) The dried polymer was dissolved in THF (288 g) and then added dropwise to methanol (3.2 L) to cause reprecipitation. (8) The polymer was recovered by suction filtration. (9) The recovered polymer was dried under reduced pressure at 50°C for 12 hours. (10) The dried polymer was recovered to obtain the final product (31.1 g).

[0045] The monomer ratio of the final copolymer was analyzed by NMR to be MMA:St = 48:52 (molar ratio). Furthermore, the molecular weight of this copolymer was analyzed by GPC to be number average molecular weight (Mn): 18,698, weight average molecular weight (Mw): 28,719, and molecular weight distribution (Mw / Mn): 1.54.

[0046] 2) Recovery of Monomer by Thermal Decomposition (1) 13.07 g of the copolymer (P(St-MMA)) synthesized in "1)" above was placed in a 30 mL quartz glass test tube, and degassing was performed by Ar flow (flow rate: 100 mL / min) for 10 minutes. (2) After degassing, the external temperature was raised to 500°C (heating rate: 10°C / min). (3) When the external temperature reached 200°C, the Ar flow rate was changed to 300 mL / min. (4) When the external temperature reached 350°C, it was confirmed that the polymer had decomposed and steam was being generated. (5) When the external temperature was between 350°C and 500°C, the liquid was collected (solution color: yellow to orange, yield: 11.4 g).

[0047] The collected liquid was subjected to 1H-NMR measurement using pyridine as an internal standard, and it was found that the liquid contained 45.5 wt% MMA and 42.8 wt% styrene.

[0048] The copolymer (P(St-MMA)) synthesized in "1)" had a molar ratio of MMA:St = 48:52 = 47:53 (weight ratio), and therefore contained 47 wt% MMA and 53 wt% styrene. Therefore, it was found that by heating the copolymer synthesized in "1)", 97 wt% of MMA and 81 wt% of styrene were recovered.

[0049] As mentioned above, Non-Patent Documents 1 and 2 report that when polystyrene polymerized using styrene as a monomer is heated, the monomer recovery rate is low at 60 to 70%, but it has been revealed that the recovery rate of styrene by heating can be improved by forming a copolymer with MMA.

[0050] 3) Recycling Synthesis (1) The styrene and methyl methacrylate mixed liquid (6.73 g) obtained in "2)" above, THF (23.8 g), and AIBN (0.067 g) were placed in a 100 ml four-neck flask and dissolved with stirring. (2) After dissolution, the flask was cooled with ice water and degassed by repeatedly reducing the pressure and leaking Ar 10 times. (3) After degassing, the flask was sealed and polymerization was carried out at an internal temperature of 65°C for 48 hours. (4) After confirming the reaction rate by 1H-NMR (approximately 50%), the reaction solution was added dropwise to methanol (275 ml) and reprecipitation was carried out. (5) The polymer was recovered by suction filtration. (6) The recovered polymer was dried under reduced pressure at 50°C for 10 hours. (7) The dried polymer was dissolved in THF (10.85 g) and then added dropwise to methanol (131.7 g) and reprecipitation was carried out. (8) The polymer was recovered by suction filtration. (9) The recovered polymer was dried under reduced pressure at 50° C. for 12 hours. (10) The dried polymer was recovered to obtain the final product (1.29 g).

[0051] The monomer ratio of the copolymer was analyzed by NMR to be MMA:St=48:52 (molar ratio). Furthermore, the molecular weight of the copolymer was analyzed by GPC to be number average molecular weight (Mn): 10,417, weight average molecular weight (Mw): 16,166, and molecular weight distribution (Mw / Mn): 1.55.

[0052] From these results, it was confirmed that a copolymer of St and MMA similar to the copolymer of St and MMA synthesized in "1)" could be obtained by resynthesis and could 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, etc., with a second monomer different from the first monomer, wherein the first monomer is methyl methacrylate (MMA) and the second monomer is styrene (St).

2. The depolymerizable copolymer according to claim 1, wherein the molar ratio of methyl methacrylate to styrene 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 280 to 500°C.

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