Depolymerizable copolymer and depolymerizable copolymer composition

Abstract

Provided is a depolymerizable copolymer that has a constituent unit derived from alpha-methylstyrene and a constituent unit derived from methyl methacrylate. The molar ratio of constituent units derived from alpha-methylstyrene and constituent units derived from methyl methacrylate is 40-70:30-60, and the weight average molecular weight is 70,000-300,000. The copolymer has a 1 / 2 method temperature of 230°C or lower as measured by the method defined in JIS K7210-1.

Description

Depolymerizable copolymer and depolymerizable copolymer composition

[0001] The present invention relates to a depolymerizable copolymer in which the polymer is decomposed into monomers by heat or light, and a composition containing the depolymerizable copolymer. In particular, the present invention relates to a depolymerizable copolymer that is less likely to leave a residue when depolymerized by heat and is easily thermoformable, and a composition containing the depolymerizable copolymer.

[0002] Technological development of plastics (polymers) has progressed as a material 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. However, at present, sufficient recycling technology has not been established, and many of them are discarded. In particular, in composite materials that combine metal and plastic, it is difficult to separate and recover the individual materials. For this reason, many of these 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 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, biodegradable polymers also pose a problem in that they take a long time to decompose, sometimes taking several months or more.

[0005] PET bottles and other items are recycled and reused. However, conventional mechanical recycling requires the addition of a certain amount of virgin polymer to prevent discoloration after repeated use. Chemical recycling also 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 for 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 developed to decompose homopolymers such as polymethyl methacrylate and polystyrene into monomers using simple methods such as heat or light (see, for example, Patent Documents 1 and 2, and Non-Patent Document 1). However, even in these cases, it is desirable to be able to thermally decompose at lower temperatures. Furthermore, since the monomer recovery rate for polystyrene is low at 60%, it is desirable to increase the monomer recovery rate.

[0007] U.S. Patent No. 9,650,313, Patent Publication No. 2006-526582

[0008] Hajime Otani et al., "Thermal Decomposition Characteristics of Polymers," Polymers, Society of Polymer Science, 46-6, 394 (1997)

[0009] An object of the present invention is to provide a depolymerizable copolymer and a depolymerizable copolymer composition which have depolymerizability, i.e., the polymer is decomposed into monomers by heat or light, and can be easily recycled, and which can be decomposed into monomers at a lower temperature with a recovery rate of 90% or more and can be thermoformed at a temperature lower than the thermal decomposition temperature.

[0010] The present inventors have found that the above-mentioned problems can be solved by a copolymer and copolymer composition containing specific monomers in a predetermined ratio and having a predetermined weight-average molecular weight, and the copolymer and copolymer composition have predetermined melting properties.

[0011] [1] A depolymerizable copolymer having a constitutional unit derived from α-methylstyrene and a constitutional unit derived from methyl methacrylate, wherein the molar ratio of the constitutional units derived from α-methylstyrene to the constitutional units derived from methyl methacrylate is 40 to 70:30 to 60, and the weight average molecular weight is 70,000 to 300,000, wherein the copolymer has a ½ method temperature of 230°C or less as measured by the method specified in JIS K7210-1.

[0012] [2] A depolymerizable copolymer composition comprising a copolymer having a weight average molecular weight of 70,000 to 300,000, which has structural units derived from α-methylstyrene and structural units derived from methyl methacrylate, wherein the molar ratio of the structural units derived from α-methylstyrene to the structural units derived from methyl methacrylate is 40 to 70:30 to 60, and a plasticizer, wherein the content of the plasticizer is 10% by weight or less relative to the copolymer, and the copolymer composition has a ½ method temperature of 230°C or less, measured according to the method specified in JIS K7210-1.

[0013] [3] The depolymerizable copolymer composition according to [2], wherein the plasticizer is tris-2-ethylhexyl trimellitate.

[0014] [4] A resin molded product using the depolymerizable copolymer according to [1] or the depolymerizable copolymer composition according to [2] or [3].

[0015] [5] A film using the depolymerizable copolymer according to [1] or the depolymerizable copolymer composition according to [2] or [3].

[0016] The depolymerizable copolymer and depolymerizable copolymer composition of the present invention are composed of or contain a copolymer obtained by copolymerizing two or more monomers constituting poly-α-methylstyrene and polymethyl methacrylate, which are homopolymers with high depolymerizability. The copolymer can be depolymerized by a simple method using heat to recover the monomers with high yields. Therefore, the depolymerizable copolymer and depolymerizable copolymer composition of the present invention can be easily recycled. Furthermore, since the depolymerizable copolymer and depolymerizable copolymer composition of the present invention leave little residue after thermal decomposition, even when a composite material is formed by combining the depolymerizable copolymer or depolymerizable copolymer composition with a different material such as a metal, the polymer can be decomposed simply by heating to recover the monomers. This enables separate recovery of the materials. Furthermore, the depolymerizable copolymer and depolymerizable copolymer composition of the present invention exhibit fluidity below their thermal decomposition temperature, allowing them to be molded without causing polymer decomposition during thermoforming, resulting in good resin molded articles. Furthermore, good films can be obtained when they are formed into films.

[0017] Hereinafter, an embodiment of the present invention will be described in detail.

[0018] The depolymerizable copolymer of the present invention has a structural unit derived from α-methylstyrene (hereinafter may be referred to as "α-methylstyrene unit") and a structural unit derived from methyl methacrylate (hereinafter may be referred to as "methyl methacrylate unit"), wherein the molar ratio of the α-methylstyrene unit to the methyl methacrylate unit is α-methylstyrene unit:methyl methacrylate unit=40 to 70:30 to 60, and the copolymer has a weight average molecular weight of 70,000 to 300,000 (hereinafter, a copolymer satisfying this monomer molar ratio and weight average molecular weight may be referred to as "the copolymer of the present invention"). The copolymer has a ½ method temperature (hereinafter may be simply referred to as "½ method temperature") of 230°C or less, measured by the method specified in JIS K7210-1.

[0019] The depolymerizable copolymer composition of the present invention is a copolymer composition comprising the copolymer of the present invention described above, i.e., a copolymer having α-methylstyrene units and methyl methacrylate units, in which the molar ratio of the α-methylstyrene units to the methyl methacrylate units is α-methylstyrene units:methyl methacrylate units=40 to 70:30 to 60, and having a weight average molecular weight of 70,000 to 300,000, and a plasticizer, wherein the content of the plasticizer is 10% by weight or less relative to the copolymer of the present invention, and the depolymerizable copolymer composition has a ½ method temperature of 230° C. or less.

[0020] The 1 / 2 method temperature in the present invention is the temperature at which 1 / 2 (half) of the resin charged into a flow tester flows out, measured in accordance with JIS K7210-1, and specifically, can be measured by the method described in the Examples section below.

[0021] [Copolymer] First, the copolymer of the present invention will be described.

[0022] The molar ratio of α-methylstyrene units to methyl methacrylate units constituting the copolymer of the present invention is α-methylstyrene units:methyl methacrylate units = 40-70:30-60. When the molar ratio of α-methylstyrene units to methyl methacrylate units is within the above range, the copolymer is easily synthesized, and a copolymer exhibiting excellent fluidity can be easily produced. From these viewpoints, the molar ratio of α-methylstyrene units to methyl methacrylate units in the copolymer of the present invention is preferably α-methylstyrene units:methyl methacrylate units = 45-65:35-55, and more preferably 55-65:35-45.

[0023] The copolymer of the present invention may contain structural units derived from monomers other than α-methylstyrene units and methyl methacrylate units (hereinafter, these may be referred to as "other monomer units"). However, if the copolymer of the present invention contains other monomer units, the depolymerization property tends to be poor. For this reason, the proportion of other monomer units contained in the copolymer of the present invention is 10 mol % or less, particularly 5 mol % or less, and most preferably 0 mol % (no other monomer units) based on 100 mol % of all monomer units constituting the copolymer of the present invention.

[0024] Examples of other monomer units that the copolymer of the present invention may contain include structural units derived from one or more of fluorine-based monomers such as tetrafluoroethylene, (meth)acrylic acid-based monomers other than methyl methacrylate such as methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, and butyl methacrylate, and styrene.

[0025] The molar ratio of the monomer units constituting the copolymer can be determined by NMR analysis.

[0026] The weight average molecular weight (Mw) of the copolymer of the present invention is within the range of 70,000 to 300,000. If Mw is below the lower limit, the polymer moldability, particularly film moldability and molded resin strength, tend to be poor. If Mw exceeds the upper limit, the depolymerization property tends to be poor. From these viewpoints, the Mw of the copolymer of the present invention is preferably 80,000 to 270,000, and more preferably 80,000 to 250,000.

[0027] The weight average molecular weight (Mw) of the copolymer is a value calculated as polystyrene by gel permeation chromatography (GPC method).

[0028] The method for producing the copolymer of the present invention is not particularly limited, and for example, a monomer mixture containing at least α-methylstyrene and methyl methacrylate may be copolymerized by a radical polymerization reaction. Specifically, the raw material monomer mixture is sealed together with a solvent containing a radical polymerization initiator, a crosslinking agent, etc. in an inert gas atmosphere, and the mixture is copolymerized by continuing to stir for a predetermined time, followed by precipitation in a poor solvent and recovery, thereby obtaining the copolymer of the present invention.

[0029] [Half-Method Temperature of Depolymerizable Copolymer] The depolymerizable copolymer of the present invention is characterized by comprising the copolymer of the present invention described above and having a half-mechanism temperature of 230°C or lower. If the half-mechanism temperature is 230°C or lower, the copolymer does not decompose at a temperature at which it exhibits good fluidity, and the copolymer exhibits excellent moldability, particularly film moldability. From the viewpoint of preventing polymer decomposition during thermoforming, the half-mechanism temperature of the depolymerizable copolymer of the present invention is preferably 210°C or lower, and more preferably 200°C or lower. On the other hand, from the viewpoint of the thermal stability of the molded material, the half-mechanism temperature of the depolymerizable copolymer of the present invention is preferably 100°C or higher, and more preferably 150°C or higher.

[0030] A copolymer having such a 1 / 2 process temperature can be produced, for example, by changing the ratio of the polymerization initiator to the monomer in the above-mentioned method for producing a copolymer of the present invention.

[0031] [Depolymerizable Copolymer Composition] The depolymerizable copolymer composition of the present invention is characterized by comprising the copolymer of the present invention described above and 10% by weight or less of a plasticizer based on the copolymer, and having a 1 / 2 method temperature of 230° C. or less. That is, even in the case of a depolymerizable copolymer having a 1 / 2 method temperature exceeding 230° C., the 1 / 2 method temperature can be lowered to 230° C. or less by adding a plasticizer. The depolymerizable copolymer composition of the present invention is a copolymer having a high 1 / 2 method temperature, and the 1 / 2 method temperature is adjusted to 230° C. or less by adding a plasticizer.

[0032] The 1 / 2 process temperature of the depolymerizable copolymer composition of the present invention is 230°C or lower, preferably 210°C or lower, more preferably 200°C or lower, and is preferably 100°C or higher, more preferably 150°C or higher, for the same reasons as the 1 / 2 process temperature of the depolymerizable copolymer of the present invention.

[0033] Examples of the plasticizer to be added to the copolymer include trimellitic ester plasticizers, pyromellitic ester plasticizers, etc. From the viewpoint of long-term durability under high temperature conditions, it is preferable to use tris-2-ethylhexyl trimellitate as the plasticizer to be added to the copolymer.

[0034] In the depolymerizable copolymer composition of the present invention, a plasticizer such as tris-2-ethylhexyl trimellitate is blended in an amount of 10% by weight or less relative to the copolymer of the present invention. If the blending amount of the plasticizer exceeds 10% by weight, the 1 / 2 process temperature decreases, but the moldability, particularly film moldability, of the resulting depolymerizable copolymer composition is impaired. The blending amount of the plasticizer varies depending on the 1 / 2 process temperature of the copolymer to which it is added, but is preferably about 5 to 10% by weight relative to the copolymer.

[0035] The depolymerizable copolymer composition of the present invention may contain any suitable additive other than a plasticizer, as needed. Examples of such additives include crosslinkers, tackifiers, pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, UV absorbers, light stabilizers, release modifiers, softeners, surfactants, flame retardants, and antioxidants. The total amount of these additives other than plasticizers is preferably 10% by weight or less, for example, 5 to 10% by weight, based on the copolymer of the present invention.

[0036] [Resin Molded Articles and Films] The depolymerizable copolymer and depolymerizable copolymer composition of the present invention can be molded into various resin molded articles and films according to conventional methods. In particular, the depolymerizable copolymer and depolymerizable copolymer composition of the present invention can be stably molded without decomposition even when thermoformed, and can easily be made into films. Furthermore, the depolymerizable copolymer and depolymerizable copolymer composition of the present invention can be used as composite molded articles with different materials such as metals, which have traditionally been difficult to recycle, and the monomers can be easily recovered by heating. Therefore, the depolymerizable copolymer and depolymerizable copolymer composition of the present invention have excellent recyclability and are highly applicable to industry.

[0037] The effects of the present invention will be more specifically illustrated below with reference to examples.

[0038] [Method for Measuring 1 / 2 Method Temperature] The 1 / 2 method temperatures of the copolymers or copolymer compositions in the Examples and Comparative Examples were measured using the apparatus and conditions shown in Table 1 below.

[0039]

[0040] [Measurement of initial elastic modulus] The method for measuring the initial elastic modulus in Example 4 and Comparative Examples 1 and 2 is as follows. Test specimens were prepared from the depolymerizable copolymer compositions obtained in Example 4 and Comparative Examples 1 and 2 using a test specimen punching machine, and tensile tests were carried out using the following equipment and conditions. The measurement was carried out three times, and the variation in the measured values ​​was also investigated. Equipment: "LTS-1kNB-s50" manufactured by Minebia. Tensile speed: 5 mm / min. Distance between chucks: 30 mm

[0041] Synthesis Examples 1 to 6: Ion-exchanged water, sodium carbonate, and "KS Soap (90% solids)" manufactured by Kao Corporation were placed in a four-neck flask and dissolved with stirring. After dissolution, a monomer mixture (α-methylstyrene (AMS), methyl methacrylate (MMA)) was added, and the system was purged with argon gas while stirring at 150 rpm. 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% pure content) were added in that order, and the mixture was stirred for 63 hours while maintaining the temperature inside the flask at 3 to 4°C. After 63 hours of stirring, 2,6-di-t-butyl-4-methylphenol was added to terminate the reaction. The reaction solution was added dropwise to methanol, and the precipitated white solid was collected by filtration. The resulting white solid was dried briefly and then dissolved in tetrahydrofuran (THF). This solution was added dropwise to methanol, and the precipitated solid was collected by filtration. The resulting white solid was dried under reduced pressure at 50°C for 48 hours to obtain the final product. Using the synthesis procedure described above, the synthesis conditions shown in Table 2 were employed to synthesize AMS / MMA copolymers A to F, respectively.

[0042]

[0043] Example 1 The monomer ratio of the AMS / MMA copolymer A obtained in Synthesis Example 1 was analyzed by NMR, and it was found to be AMS:MMA = 60:40 (molar ratio). The molecular weight of this AMS / MMA copolymer A was analyzed by GPC, and it was found to be a weight average molecular weight (Mw): about 126,000. The obtained AMS / MMA copolymer was analyzed (N ２When heated in a 100°C (100°C / min) environment, the decomposition onset temperature was approximately 200°C, the decomposition completion temperature was approximately 350°C, the decomposition rate was 100%, and no residue was observed. Similar results were obtained by thermogravimetric differential thermal analysis of AMS / MMA copolymers B to F obtained in Synthesis Examples 2 to 6. With continued heating, typical polymers gradually decompose from the ends of the polymer molecules, causing discoloration and ultimately leaving behind black residue. However, the AMS / MMA copolymer did not show such decomposition-related discoloration and was confirmed to completely decompose into monomers, confirming its high depolymerization properties. The half-wave temperature of AMS / MMA copolymer A was measured and found to be 221°C. AMS / MMA copolymer A was dissolved in tetrahydrofuran (THF), poured into a glass Petri dish, and slowly dried. Visual observation confirmed the formation of a film.

[0044] Example 2 The AMS / MMA copolymer A obtained in Synthesis Example 1 was dissolved in tetrahydrofuran (THF), and tris-2-ethylhexyl trimellitate was added as a plasticizer in an amount of 5 wt % based on the AMS / MMA copolymer A to prepare an AMS / MMA copolymer A composition. This AMS / MMA copolymer A composition was poured into a glass petri dish and slowly dried. Observation of the appearance confirmed that a film had been formed. The ½ method temperature of the AMS / MMA copolymer A composition after the addition of tris-2-ethylhexyl trimellitate was measured and found to be 198°C.

[0045] Example 3 The AMS / MMA copolymer A obtained in Synthesis Example 1 was dissolved in tetrahydrofuran (THF), and tris-2-ethylhexyl trimellitate was added as a plasticizer in an amount of 10 wt % based on the AMS / MMA copolymer A to prepare an AMS / MMA copolymer A composition. This AMS / MMA copolymer A composition was poured into a glass petri dish and slowly dried. Observation of the appearance confirmed that a film had been formed. The ½ method temperature of the AMS / MMA copolymer A composition after the addition of tris-2-ethylhexyl trimellitate was measured and found to be 182°C.

[0046] Comparative Example 1 The monomer ratio of AMS / MMA copolymer B obtained in Synthesis Example 2 was analyzed by NMR, and it was found to be AMS:MMA = 60:40 (molar ratio). The molecular weight of this AMS / MMA copolymer B was analyzed by GPC, and it was found to be a weight average molecular weight (Mw) of approximately 263,000. The 1 / 2 method temperature of AMS / MMA copolymer B was measured and found to be 245°C. The fluidity of AMS / MMA copolymer B at 245°C was evaluated, and decomposition of the resin was observed.

[0047] AMS / MMA copolymer B was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. The appearance of the resulting solution confirmed the formation of a film. The initial modulus of elasticity of AMS / MMA copolymer B was measured, and the results were stable, ranging from 1700 to 2000 MPa, over three measurements.

[0048] Example 4 The AMS / MMA copolymer B obtained in Synthesis Example 2 was dissolved in tetrahydrofuran (THF), and tris-2-ethylhexyl trimellitate was added as a plasticizer in an amount of 10 wt % relative to the AMS / MMA copolymer B to prepare an AMS / MMA copolymer B composition. This AMS / MMA copolymer B composition was poured into a glass petri dish and slowly dried. The appearance was observed, confirming the formation of a film. The half-wave temperature of the AMS / MMA copolymer B composition after the addition of tris-2-ethylhexyl trimellitate was measured and found to be 195°C. The fluidity of this AMS / MMA copolymer B composition at 195°C was evaluated, and no resin decomposition was observed. The initial modulus of the AMS / MMA copolymer B composition was measured three times, and the initial modulus was found to be 1900 to 2000 MPa, a stable value comparable to that of Comparative Example 1.

[0049] Comparative Example 2 The AMS / MMA copolymer B obtained in Synthesis Example 2 was dissolved in tetrahydrofuran (THF), and tris-2-ethylhexyl trimellitate was added as a plasticizer in an amount of 20 wt % relative to the AMS / MMA copolymer B to prepare an AMS / MMA copolymer B composition. This AMS / MMA copolymer B composition was poured into a glass petri dish and slowly dried. The appearance was observed, confirming the formation of a film. The half-wave temperature of the AMS / MMA copolymer B composition after the addition of tris-2-ethylhexyl trimellitate was measured and found to be 185°C. The fluidity of this AMS / MMA copolymer B composition at 185°C was evaluated, and no resin decomposition was observed. The initial modulus of the AMS / MMA copolymer B composition was measured, and the initial modulus varied widely from 1500 to 2000 MPa across three measurements, indicating that a uniform resin composition had not been formed.

[0050] Comparative Example 3 The monomer ratio of the AMS / MMA copolymer C obtained in Synthesis Example 3 was analyzed by NMR, revealing that the molar ratio was AMS:MMA = 65:35. The molecular weight of this AMS / MMA copolymer C was analyzed by GPC, revealing that the weight average molecular weight (Mw) was approximately 28,000. The 1 / 2 method temperature of the AMS / MMA copolymer C was measured and found to be 187°C. The AMS / MMA copolymer C was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. Upon observing the appearance, it was confirmed that cracks were present and that a film could not be formed.

[0051] Comparative Example 4 The monomer ratio of AMS / MMA copolymer D obtained in Synthesis Example 4 was analyzed by NMR, and it was found to be AMS:MMA = 60:40 (molar ratio). The molecular weight of this AMS / MMA copolymer D was analyzed by GPC, and it was found to be a weight average molecular weight (Mw) of approximately 34,000. The 1 / 2 method temperature of AMS / MMA copolymer D was measured and found to be 190°C. AMS / MMA copolymer D was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. Upon observing the appearance, it was found to have cracks and could not be used to form a film.

[0052] Comparative Example 5 The monomer ratio of the AMS / MMA copolymer E obtained in Synthesis Example 5 was analyzed by NMR, and it was found to be AMS:MMA = 50:50 (molar ratio). The molecular weight of this AMS / MMA copolymer E was analyzed by GPC, and it was found to be a weight average molecular weight (Mw) of approximately 26,000. The 1 / 2 process temperature of the AMS / MMA copolymer E was measured and found to be 230°C. The AMS / MMA copolymer E was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. Upon observing the appearance, it was found to have cracks and could not be used to form a film.

[0053] Comparative Example 6 AMS / MMA copolymer D composition was prepared by dissolving the AMS / MMA copolymer D obtained in Synthesis Example 4 in tetrahydrofuran (THF) and adding tris-2-ethylhexyl trimellitate as a plasticizer in an amount of 10 wt % based on the AMS / MMA copolymer D. This AMS / MMA copolymer D composition was poured into a glass petri dish and slowly dried. Upon observing the appearance, cracks were found to have occurred, and no film could be formed. The 1 / 2 method temperature of the AMS / MMA copolymer D composition after the addition of tris-2-ethylhexyl trimellitate was measured and found to be 154°C.

[0054] Comparative Example 7 AMS / MMA copolymer D composition was prepared by dissolving the AMS / MMA copolymer D obtained in Synthesis Example 4 in tetrahydrofuran (THF), and adding tris-2-ethylhexyl trimellitate as a plasticizer in an amount of 20% by weight based on the AMS / MMA copolymer D. This AMS / MMA copolymer D composition was poured into a glass petri dish and slowly dried. Upon observing the appearance, cracks were found to have occurred, and no film could be formed.

[0055] Comparative Example 8 The monomer ratio of AMS / MMA copolymer F obtained in Synthesis Example 6 was analyzed by NMR, and it was found to be AMS:MMA = 60:40 (molar ratio). The molecular weight of this AMS / MMA copolymer F was analyzed by GPC, and it was found to be a weight average molecular weight (Mw) of approximately 51,000. The 1 / 2 method temperature of AMS / MMA copolymer F was measured and found to be 208°C. AMS / MMA copolymer F was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. Upon observing the appearance, it was found to have cracks and could not be used to form a film.

[0056] Comparative Example 9 As an example of a polymer with low depolymerization property, TG-DTA analysis of polycarbonate (N ２As 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 finished at about 550°C. The decomposition proceeded to about 70%, but about 30% remained undecomposed as residue.

[0057] Comparative Example 10 TG-DTA analysis (N ２ As a result of the test, it was observed that the decomposition started at about 300°C and ended at about 400°C, and no residue was left behind.

[0058] The results of Examples 1 to 4 and Comparative Examples 1 to 10 are summarized in the following Table 3. Table 3 also lists the number average molecular weight (Mn) and dispersity (Mw / Mn) obtained when measuring the weight average molecular weight (Mw) of each AMS / MMA copolymer.

[0059]

[0060] [Results and Discussion] Comparing Comparative Example 9 with Examples 1 to 4 and Comparative Examples 1 to 8, it was confirmed that Examples 1 to 4 and Comparative Examples 1 to 8 decomposed at a lower temperature than Comparative Example 9, i.e., a decomposition start temperature of 200°C and a decomposition end temperature of 350°C, in TG-DTA analysis, and had depolymerizability without leaving any residue. Comparing Comparative Example 10 with Examples 1 to 4 and Comparative Examples 1 to 8, it was confirmed that Examples 1 to 4 and Comparative Examples 1 to 8 decomposed at a lower temperature than Comparative Example 10, i.e., a decomposition start temperature of 200°C and a decomposition end temperature of 350°C, in TG-DTA analysis, and had depolymerizability without leaving any residue.

[0061] Comparing Example 1 with Comparative Examples 1, 4, and 8, it is clear that a film can be formed with a weight-average molecular weight (Mw) of 70,000 or more. However, in Comparative Example 1, the 1 / 2 process temperature was 245°C, and it is clear that at the temperature (= 1 / 2 process temperature) at which good fluidity is exhibited, the resin decomposes, making thermoforming difficult.

[0062] Comparing Examples 1, 2, and 3 with Comparative Examples 1, 2, and 4, it was confirmed that the 1 / 2 process temperature can be reduced by adding a plasticizer. However, when the plasticizer was added in an amount of 20% by weight relative to the copolymer, the formed film did not exhibit stable performance. This indicates that the optimal amount of plasticizer to be added is 10% by weight or less relative to the copolymer.

[0063] Comparing Comparative Examples 3, 4, and 5, it can be seen that the higher the molar ratio of α-methylstyrene (AMS), the lower the 1 / 2 process temperature, and a copolymer exhibiting good fluidity at a lower temperature can be obtained. At an AMS:MMA ratio of 50:50, the 1 / 2 process temperature was as high as 230°C, and it was found that at the temperature at which good fluidity was exhibited (= 1 / 2 process temperature), the resin decomposed, making thermoforming difficult. Furthermore, because AMS has low reactivity, increasing the AMS ratio required increasing the amount of AMS charged. At an AMS:MMA ratio of 65:35, a large amount of AMS remained unreacted during synthesis. It can be seen that the upper limit of the AMS ratio at which little unreacted AMS remained during the reaction and good fluidity was exhibited was an AMS:MMA ratio of 60:40.

[0064] In Comparative Example 7, even when 20% by weight of plasticizer was added to the copolymer, film formation was difficult, which shows that film formation is difficult even when a plasticizer is added to a copolymer with a low molecular weight.

[0065] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-202975, filed on November 30, 2023, and is incorporated by reference in its entirety.

Claims

1. A depolymerizable copolymer having a constitutional unit derived from α-methylstyrene and a constitutional unit derived from methyl methacrylate, in which the molar ratio of the constitutional units derived from α-methylstyrene to the constitutional units derived from methyl methacrylate is 40-70:30-60, and the weight average molecular weight is 70,000 to 300,000, wherein the copolymer has a 1 / 2 method temperature of 230°C or less as measured by the method specified in JIS K7210-1.

2. A depolymerizable copolymer composition comprising a copolymer having a weight average molecular weight of 70,000 to 300,000, which has a structural unit derived from α-methylstyrene and a structural unit derived from methyl methacrylate, and in which the molar ratio of the structural units derived from α-methylstyrene to the structural units derived from methyl methacrylate is 40-70:30-60, and a plasticizer, wherein the content of the plasticizer is 10% by weight or less relative to the copolymer, and the copolymer composition has a 1 / 2 method temperature of 230°C or less, measured according to the method specified in JIS K7210-1.

3. The depolymerizable copolymer composition according to claim 2, wherein said plasticizer is tris-2-ethylhexyl trimellitate.

4. A resin molded product using the depolymerizable copolymer according to claim 1 or the depolymerizable copolymer composition according to claim 2 or 3.

5. A film using the depolymerizable copolymer according to claim 1 or the depolymerizable copolymer composition according to claim 2 or 3.

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