Depolymerizable copolymer

Abstract

To provide a copolymer which 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.SOLUTION: The depolymerizable copolymer is obtained by copolymerizing a first monomer, which constitutes a depolymerizable homopolymer capable of being decomposed into the monomer by heating, light or the like, and a second monomer, which is different from the first monomer, where the first monomer is methyl methacrylate (MMA) and the second monomer is styrene (St). Preferably, 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.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a copolymer having a depolymerization property in which a polymer is decomposed into monomers by heat or light, and particularly to a copolymer having a depolymerization property in which hardly any residue remains when depolymerized by heat.

Background Art

[0002] Plastic (polymer) has been developed as a material with excellent durability and heat resistance, and various materials are used in the market. On the other hand, these plastic materials are not naturally decomposed in the environment. For this reason, although their impact on the environment has been pointed out, at present, since sufficient recycling technologies have not been established, many of them are discarded. In particular, in the case of composite materials in which metal and plastic are combined, it is difficult to separate and recover each material, and at present, many of them are landfilled.

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

[0004] However, regarding biodegradable polymers, the safety of substances during biodegradation in the environment, the fact that substances during decomposition become microplastics, and the effects when these are ingested by environmental organisms and marine organisms are not clear. Furthermore, although biodegradable polymers have a certain effect on waste reduction, regarding the issue of reuse, there are also problems such as the low physical properties of recycled products, and the fundamental problems have not been solved. Furthermore, from the perspective of waste reduction, there is also a problem that the time until decomposition is long, and in some cases, it may take several months or more.

[0005] In addition, PET bottles and the like are recycled and reused. However, in conventional mechanical recycling, since they become colored when repeatedly used, it is necessary to add a certain amount of virgin polymer. Further, in order to perform chemical recycling, it is necessary to decompose them into monomers using special chemicals and the like, which requires a great deal of labor and energy. Furthermore, there is also a problem that the uses of recycled products are limited.

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

[0007] However, even in this case, it is desired that thermal decomposition can be performed at a lower temperature. Further, for polystyrene, since the monomer recovery rate in thermal decomposition is as low as 60 to 70%, it is desired to increase the monomer recovery rate (Non-Patent Document 1, Non-Patent Document 2).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0009]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide a depolymerizable copolymer that has a depolymerizability in which a polymer is decomposed into monomers by heat or light and is easily recyclable.

Means for Solving the Problems

[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 or light, and 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 such an invention (Invention 1), it has been found that by copolymerizing styrene (St) with methyl methacrylate (MMA) that constitutes a homopolymer with high depolymerizability, a depolymerizable copolymer that is easy to recycle, has little residue during heating, and has high convenience can be obtained. Although homopolymers having depolymerizability have been known so far, the characteristics of polymers obtained by copolymerizing a monomer constituting a homopolymer having depolymerizability and another monomer have not been clear. Therefore, as a result of intensive studies by the present inventors on polymers obtained by copolymerizing a monomer constituting a homopolymer having depolymerizability and another monomer, it has been confirmed that the copolymer described in Invention 1 has depolymerizability, and further, no residue remains due to thermal decomposition, and the monomers constituting it can be completely recovered by thermal decomposition.

[0013] In the above invention (Invention 1), it is preferable that the molar ratio of methyl methacrylate to styrene in the depolymerizable copolymer is 10:90 to 90:10 (Invention 2).

[0014] According to such an invention (Invention 2), a more convenient depolymerizable copolymer polymer can be obtained, which has depolymerizability, leaves no residue upon thermal decomposition, and can completely recover the monomers that constitute it by thermal decomposition.

[0015] Further, in the above invention (Invention 1), it is preferable that the weight average molecular weight (Mw) of the depolymerizable copolymer polymer is 5,000 to 1,000,000 (Invention 3).

[0016] According to such an invention (Invention 3), a more convenient depolymerizable copolymer polymer can be obtained, which has depolymerizability, leaves no residue upon thermal decomposition, and can completely recover the monomers that constitute it by thermal decomposition.

[0017] Furthermore, in the above inventions (Inventions 1 to 3), it is preferable that the thermal decomposition temperature of the depolymerizable copolymer polymer is 280 to 500 °C (Invention 4).

[0018] According to such an invention (Invention 4), a depolymerizable copolymer polymer can be obtained, which has depolymerizability, leaves no residue upon thermal decomposition, can completely recover the monomers that constitute it by thermal decomposition, is highly convenient, and has good handleability.

Advantages of the Invention

[0019] The depolymerizable copolymer polymer of the present invention is a copolymer of methyl methacrylate (MMA) as the first monomer constituting a depolymerizable homopolymer that decomposes into monomers by heating or light, and styrene (St) as the second monomer. Since the monomers can be recovered in a high yield by a simple method of heating, recycling is easy. In addition, since there is little residue after thermal decomposition, even when a heterogeneous material such as metal is combined with this polymer to form a composite material, the polymer can be decomposed by heating alone to recover the monomers, enabling separate recovery of the materials.

Modes for Carrying Out the Invention

[0020] The depolymerizable copolymer polymer 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 predetermined monomer alone, and is preferably decomposed into monomers by heating, light, etc., and has an extremely high recovery rate of 90% or more of the monomer recovery rate. As such a depolymerizable homopolymer with a high monomer recovery rate, polymethyl methacrylate (PMMA), poly-α-methylstyrene (PAMS), polytetrafluoroethylene (PTFE), etc. are known. The monomers (monomer components) constituting 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 constituting the depolymerizable homopolymer as a raw material.

[0022] (Second monomer) In the depolymerizable copolymer polymer of the present invention, styrene (St) is used as the second monomer copolymerized with methyl methacrylate (MMA).

[0023] (Characteristics of depolymerizable copolymer polymer) The depolymerizable copolymer polymer 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 polymer composed of MMA:St 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 preferable.

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

[0025] Furthermore, the thermal decomposition temperature of the depolymerizable copolymer of the present invention is not particularly limited as long as it can be thermally decomposed, but is preferably 280°C to 500°C, particularly preferably 290 to 450°C.

[0026] Any appropriate additive may be blended with the depolymerizable copolymer as needed. Examples of such additives include crosslinking agents, tackifiers, plasticizers (e.g., trimellitic acid ester-based plasticizers, pyromellitic acid ester-based plasticizers, etc.), pigments, dyes, fillers, anti-aging agents, conductive materials, antistatic agents, ultraviolet absorbers, light stabilizers, peeling regulators, softeners, surfactants, flame retardants, antioxidants, and the like.

[0027] (Method for producing a depolymerizable copolymer) The method for producing the depolymerizable copolymer is not particularly limited. For example, it may be copolymerized by a radical polymerization reaction. Specifically, the raw material monomers are sealed in an inert gas atmosphere together with a solvent mixed with a radical polymerization initiator, a crosslinking agent, etc., and copolymerized by continuously stirring for a long time, and then precipitated in a poor solvent and recovered to produce it.

[0028] As described above, the depolymerizable copolymer of the present invention has been described. The present invention is a depolymerizable copolymer obtained by copolymerizing a first monomer that constitutes a depolymerizable homopolymer that decomposes into monomers by heating, light, etc., and a second monomer different from this. The first monomer is methyl methacrylate (MMA), and the second monomer is styrene (St). This depolymerizable copolymer can easily recover monomers by heating even as a molded body with a different material such as metal that was conventionally difficult to recycle, so it has excellent recyclability and its industrial applicability is extremely large.

Examples

[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 a 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 charged into a 500-ml four-necked flask and dissolved with stirring. (2) After dissolution, degassing was performed by repeating the vacuum / Ar leak 10 times while cooling with ice water. (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 by 1H-NMR (about 60%), the reaction solution was dropped into 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 dissolving the polymer dried under reduced pressure in THF (263.6 g), it was dropped into methanol (3.7 L) for 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, TG-DTA Analysis of the Depolymerizable Copolymer) When the monomer ratio of the copolymer obtained in Example 1 was analyzed by NMR, it was found to be MMA:St = 47:53 (molar ratio). Also, when the molecular weight of this copolymer was analyzed by GPC, the number-average molecular weight (Mn) was 16134, the weight-average molecular weight (Mw) was 29943, and the molecular weight distribution (Mw / Mn) was 1.86. Furthermore, the obtained copolymer was analyzed by a thermogravimetric differential thermal analyzer (TG-DTA) capable of image observation (N 2When the environment was heated at a rate of 10 °C / min, the decomposition start temperature was about 290 °C, the 50% decomposition temperature was about 390 °C, and the decomposition end temperature was about 430 °C. For general polymers, due to continuous heating, they gradually decompose from the ends of the polymer molecules, resulting in discoloration and finally leaving black residues. However, the copolymer polymer of Example 1 did not show such discoloration associated with decomposition, and it was confirmed that it completely decomposed into monomers, indicating high depolymerization ability. The TG-DTA analysis results of the copolymer polymer (P(St-MMA)) of Example 1 are shown in Table 1.

[0032] [Comparative Example 1] (TG-DTA Analysis of Polycarbonate) As an example of a polymer with low depolymerization ability, TG-DTA analysis of polycarbonate (N 2 When the environment was heated at a rate of 10 °C / min, the decomposition start temperature was about 400 °C, and it gradually changed to black. The decomposition end temperature was about 550 °C. It was observed that the decomposition proceeded to about 70%, but about 30% remained undecomposed as residues.

[0033] [Comparative Example 2] (TG-DTA Analysis of Polystyrene) TG-DTA analysis (N of polystyrene polymerized from styrene, which is the second monomer component of the copolymer polymer synthesized in Example 1 2 When the environment was heated at a rate of 10 °C / min, the decomposition start temperature was about 360 °C, the 50% decomposition temperature was about 410 °C, and the decomposition end temperature was about 440 °C. There was no residue after heating. The TG-DTA analysis results of this polystyrene (PSt) are shown together with Table 1.

[0034]

Table 1

[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 a polymer of the second monomer component.

[0036] [Example 3] (TG-DTA Analysis of the Depolymerizable Copolymer) As a result of performing TG-DTA analysis (in an N 2 environment with a heating rate of 10 °C / min) on the copolymer synthesized in Example 1, heating it up to 400 °C and then maintaining the temperature at 400 °C, it was confirmed that the decomposition was completed within 30 minutes of temperature maintenance and there was no residue. That is, it was found that the copolymer of Example 1 could be completely decomposed by heating and maintaining at 400 °C.

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

[0038]

Table 2

[0039]

Table 3

[0040]

Table 4

[0041] [Comparative Example 3] (TG-DTA / MS Analysis of Polystyrene) When mass spectrometry of the pyrolysis gas (TG-DTA / GC-MS) was performed on polystyrene in the same manner as in Example 2, it was reported that 70% was styrene, which is a monomer, and the remaining was detected as dimers and trimers of styrene, and styrene could not be completely recovered.

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

[0043] [Example 5] (Thermal decomposition monomer recovery and recycling synthesis of depolymerizable copolymer) 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 components were cooled to room temperature to obtain a liquid component. As a result of synthesizing a polymer from this liquid component in the same manner as in Example 1, a copolymer of St and MMA similar to that of Example 1 was obtained, and it was confirmed that it can be reused.

[0044] [Example 6] (Synthesis of depolymerizable copolymer, monomer recovery by thermal decomposition, 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-necked flask and dissolved with stirring. (2) After dissolution, vacuum / Ar leak was repeated 10 times while cooling with ice water to perform degassing. (3) After degassing, it was sealed and polymerized at an internal temperature of 65 °C for 48 hours. (4) After confirming the reaction rate by 1H-NMR (it was about 70%), the reaction solution was dropped into 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 dissolving the dried polymer in THF (288 g), it was dropped into methanol (3.2 L) for 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] When the monomer ratio of the copolymer in the final product was analyzed by NMR, it was found to be MMA:St = 48:52 (molar ratio). Also, when the molecular weight of this copolymer was analyzed by GPC, the number average molecular weight (Mn) was 18,698, the weight average molecular weight (Mw) was 28,719, and the molecular weight distribution (Mw / Mn) was 1.54.

[0046] 2) Recovery of monomers by thermal decomposition (1) 13.07 g of the copolymer (P(St-MMA)) synthesized in the above “1)” was charged into a 30 mL quartz glass test tube, and an Ar flow (flow rate: 100 mL / min) was carried out for 10 minutes for degassing. (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 was decomposed and vapor was coming out. (5) The liquid was collected at an external temperature of 350 °C to 500 °C (color of the solution: yellow to orange, yield: 11.4 g)

[0047] For the liquid collected in this way, 1H-NMR measurement was carried out using pyridine as an internal standard. As a result, it was found that the liquid contained 45.5 wt% of MMA and 42.8 wt% of styrene, respectively.

[0048] The copolymer (P(St-MMA)) synthesized in “1)” has MMA:St = 48:52 (molar ratio) = 47:53 (weight ratio), so it contains 47 wt% of MMA and 53 wt% of styrene. Therefore, it was found that by heating the copolymer synthesized in “1)”, 97 wt% of MMA and 81 wt% of styrene could be recovered.

[0049] As described above, in Non-Patent Document 1 and Non-Patent Document 2, it has been reported that polystyrene polymerized with styrene as a monomer has a low monomer recovery rate of 60-70% when heated. However, it has been clarified that the recovery rate of styrene by heating is improved by making it a copolymer with MMA.

[0050] 3) Recycling synthesis (1) Into a 100 ml four-necked flask, the mixed liquid of styrene and methyl methacrylate (6.73 g) obtained in the above-mentioned “2)”, THF (23.8 g) and AIBN (0.067 g) were charged and dissolved with stirring. (2) After dissolution, while cooling with ice water, decompression / Ar leak was repeated 10 times to perform degassing. (3) After degassing, it was sealed and polymerized at an internal temperature of 65 °C for 48 hours. (4) After confirming the reaction rate by 1H-NMR (it was about 50%), the reaction solution was dropped into methanol (275 ml) 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 dissolving the dried polymer in THF (10.85 g), it was dropped into methanol (131.7 g) for 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 (1.29 g).

[0051] When the monomer ratio of the above copolymer was analyzed by NMR, it was MMA:St = 48:52 (molar ratio). Also, when the molecular weight of this copolymer was analyzed by GPC, the number average molecular weight (Mn): 10417, the weight average molecular weight (Mw): 16166, and the 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)” was obtained by resynthesis and that it can be reused.

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, 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 depolymerizable copolymer has a thermal decomposition temperature of 280 to 500°C.

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