Depolymerizable copolymer and depolymerizable copolymer composition

Abstract

To provide a depolymerizable 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, where the depolymerizable copolymer can depolymerize into monomers at a recovery rate of 90% or more at a lower temperature and can also be thermally molded at a temperature lower than the thermal decomposition temperature.SOLUTION: The depolymerizable copolymer that has a constituent unit derived from α-methylstyrene and a constituent unit derived from methyl methacrylate. The molar ratio between constituent units derived from α-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 less as measured by the method defined in JIS K7210-1.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 a copolymer composition, and particularly relates to a copolymer and a copolymer composition having a depolymerization property that hardly leaves residues when depolymerized by heat and is easily thermoformed.

Background Art

[0002] Plastics (polymers) have been developed as materials 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 increasing interest in SDGs, various efforts have been made to develop technologies for decomposing plastics such as biodegradable polymers and to recycle and reuse plastics.

[0004] However, in the case of biodegradable polymers, the environmental safety of substances during biodegradation, 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, there are also problems such as the low physical properties of recycled products regarding the issue of reuse, 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, although PET bottles and the like are recycled and reused, in conventional mechanical recycling, since they are 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, and there are problems that it 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 Documents 1 and 2, Non-Patent Document 1). 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 is as low as 60%, it is desired to increase the monomer recovery rate.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0008]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of the above problems, and is a copolymer having a depolymerization property in which a polymer is decomposed into monomers by heat or light, and is easily recyclable. It can be decomposed into monomers with a recovery rate of 90% or more at a lower temperature, and an object thereof is to provide a depolymerizable copolymer and a depolymerizable copolymer composition capable of thermoforming at a temperature lower than the thermal decomposition temperature. [Means for Solving the Problems]

[0010] As a result of repeated studies to solve the above problems, the present inventors have found that a copolymer and a composition thereof using specific monomers at a predetermined ratio and having a predetermined weight average molecular weight, and a copolymer and a copolymer composition having predetermined melting characteristics can solve the above problems. That is, the gist of the present invention is as follows.

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

[0012] [2] A copolymer composition containing a copolymer having a structural unit derived from α-methylstyrene and a structural unit derived from methyl methacrylate, wherein the molar ratio of the structural unit derived from α-methylstyrene to the structural unit derived from methyl methacrylate is 40 to 70:30 to 60, and the weight average molecular weight is 70,000 to 300,000, and a plasticizer, The content of the plasticizer is 10% by weight or less based on the copolymer, The copolymer composition is a depolymerizable copolymer composition having a half-life temperature of 230 ° C. or lower measured by the method defined 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 article 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]. [Advantages of the Invention]

[0016] The depolymerizable copolymer and the depolymerizable copolymer composition of the present invention are composed of a copolymer obtained by copolymerizing two or more monomers constituting poly-α-methylstyrene and polymethyl methacrylate, which are homopolymers having high depolymerizability, or include this copolymer, and can be depolymerized by a simple method by heating to recover monomers in a high yield. Therefore, the depolymerizable copolymer and the depolymerizable copolymer composition of the present invention can be easily recycled. In addition, since there is little residue after thermal decomposition, even when a dissimilar material such as metal is combined with this depolymerizable copolymer or depolymerizable copolymer composition to form a composite material, the polymer can be decomposed by heating to recover the monomers, enabling separate recovery of the materials. Furthermore, since the depolymerizable copolymer and the depolymerizable copolymer composition of the present invention exhibit fluidity below the thermal decomposition temperature, it is possible to perform molding without causing decomposition of the polymer during thermoforming, and a good resin molded article can be obtained. Also, when formed into a film, a good film can be obtained. [Embodiments for Carrying Out the Invention]

[0017] Hereinafter, embodiments 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"), and 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 it is a copolymer having a weight average molecular weight of 70,000 to 300,000 (hereinafter, the copolymer satisfying this monomer molar ratio and weight average molecular weight may be referred to as "the copolymer of the present invention"), and the copolymer is a depolymerizable copolymer having a half-life temperature (hereinafter, may be simply referred to as "half-life temperature") measured by the method defined in JIS K7210-1 of 230°C or lower. The depolymerizable copolymer composition of the present invention is a copolymer composition containing the above copolymer of the present invention, that is, a copolymer having an α-methylstyrene unit and a methyl methacrylate unit, and 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 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 based on the copolymer of the present invention, and it is a depolymerizable copolymer composition having a half-life temperature of 230°C or lower.

[0019] The half-life temperature in the present invention is the temperature at which half (one-half) of the resin charged into the flow tester flows out, measured in accordance with JIS K7210-1, and specifically, it can be measured by the method described in the Examples section below.

[0020] [Copolymer] First, the copolymer of the present invention will be described.

[0021] The molar ratio of the α-methylstyrene unit to the methyl methacrylate unit constituting the copolymer of the present invention is α-methylstyrene unit:methyl methacrylate unit = 40 to 80:30 to 60. If the molar ratio of the α-methylstyrene unit to the methyl methacrylate unit is within the above range, the synthesis of the copolymer is easy, and a copolymer having excellent fluidity can be easily produced. From these viewpoints, the molar ratio of the α-methylstyrene unit to the methyl methacrylate unit of the copolymer of the present invention is preferably α-methylstyrene unit:methyl methacrylate unit = 50 to 70:35 to 55, and more preferably 55 to 65:35 to 45.

[0022] The copolymer of the present invention may contain a structural unit derived from a monomer other than the α-methylstyrene unit and the methyl methacrylate unit (hereinafter, may be referred to as "other monomer unit"). However, when the copolymer of the present invention contains other monomer units, the depolymerization property tends to be inferior. Therefore, the proportion of other monomer units contained in the copolymer of the present invention is 10 mol% or less, particularly 5 mol% or less, in 100 mol% of all monomer units constituting the copolymer of the present invention, and 0 mol% (not containing other monomer units) is most preferable.

[0023] Examples of other monomer units that the copolymer of the present invention may contain include structural units derived from one or more fluorine-based monomers such as tetrafluoroethylene, (meth)acrylic acid-based monomers such as methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, and butyl methacrylate, and styrene.

[0024] The molar ratio of the monomer units constituting the copolymer can be determined by NMR analysis.

[0025] The weight average molecular weight (Mw) of the copolymer polymer of the present invention is in the range of 70,000 to 300,000. If Mw is less than the above lower limit, the moldability as a polymer, particularly the film moldability and the strength of the molded resin, tend to be inferior. If it exceeds the above upper limit, the depolymerization property tends to be inferior. From such a viewpoint, the Mw of the copolymer polymer of the present invention is preferably 80,000 to 270,000, and more preferably 80,000 to 250,000.

[0026] Incidentally, the weight average molecular weight (Mw) of the copolymer polymer is a value in terms of polystyrene by gel permeation chromatography (GPC method).

[0027] There is no particular limitation on the method for producing the copolymer polymer of the present invention. For example, a monomer mixture containing at least α-methylstyrene and methyl methacrylate may be copolymerized by a radical polymerization reaction. Specifically, the monomer mixture as a raw material is 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 predetermined time, and then precipitated and recovered in a poor solvent to obtain the copolymer polymer of the present invention.

[0028] [Depolymerizable copolymer polymer] The depolymerizable copolymer polymer of the present invention is composed of the above-mentioned copolymer polymer of the present invention and is characterized in that the half-life temperature is 230°C or lower. If the half-life temperature is 230°C or lower, the copolymer polymer decomposes at a temperature showing good fluidity, and the moldability, particularly the film moldability, is excellent. From the viewpoint of preventing the polymer from decomposing during thermoforming, the half-life temperature of the depolymerizable copolymer polymer 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-life temperature of the depolymerizable copolymer polymer of the present invention is preferably 100°C or higher, and more preferably 150°C or higher.

[0029] A copolymer having such a half-life temperature can be produced, for example, in the method for producing the copolymer of the present invention described above, by changing the ratio of the polymerization initiator to the monomer.

[0030] [Depolymerizable copolymer composition] The depolymerizable copolymer composition of the present invention contains the copolymer of the present invention described above and a plasticizer of 10% by weight or less based on the copolymer, and is characterized in that the half-life temperature is 230°C or lower. That is, even a depolymerizable copolymer having a half-life temperature exceeding 230°C can have its half-life temperature lowered to 230°C or lower by adding a plasticizer. The depolymerizable copolymer composition of the present invention is obtained by adjusting the half-life temperature to 230°C or lower by adding a plasticizer to a copolymer having a high half-life temperature.

[0031] For the same reasons as the half-life temperature of the depolymerizable copolymer of the present invention, the half-life 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, preferably 100°C or higher, more preferably 150°C or higher.

[0032] Examples of the plasticizer added to the copolymer include trimellitic acid ester plasticizers and pyromellitic acid ester plasticizers. From the viewpoint of long-term durability under high-temperature conditions, it is preferable to use tris(2-ethylhexyl) trimellitate.

[0033] In the depolymerizable copolymer composition of the present invention, a plasticizer such as tris(2-ethylhexyl) trimellitate is blended in a ratio of 10% by weight or less based on the copolymer of the present invention. When the blending amount of the plasticizer exceeds 10% by weight, the half-life temperature decreases, but the moldability of the resulting depolymerizable copolymer composition, particularly the film moldability, is impaired. The blending amount of the plasticizer varies depending on the half-life temperature of the copolymer to which it is added, but it is preferably about 5 to 10% by weight based on the copolymer.

[0034] In the depolymerizable copolymer composition of the present invention, any appropriate additive other than the plasticizer may be blended as necessary. Examples of such additives include crosslinking agents, tackifiers, pigments, dyes, fillers, anti-aging agents, conductive materials, antistatic agents, ultraviolet absorbers, light stabilizers, peeling regulators, softeners, surfactants, flame retardants, antioxidants, and the like. The blending amount of these additives other than the plasticizer is preferably 10% by weight or less, for example, 5 to 10% by weight, based on the copolymer of the present invention as the total amount.

[0035] [Resin Moldings and Films] The depolymerizable copolymer and the depolymerizable copolymer composition of the present invention can be formed into various resin moldings and films according to a conventional method. In particular, the depolymerizable copolymer and the depolymerizable copolymer composition of the present invention can be stably formed without decomposition even when thermoformed, and can be easily formed into a film. In addition, since monomers can be easily recovered by heating even in a composite molded body with a different material such as metal, which was conventionally difficult to recycle, it has excellent recyclability and its industrial applicability is extremely large.

Examples

[0036] Hereinafter, examples are given to more specifically show the effects of the present invention.

[0037] [Measurement Method of Half-Life Temperature] The half-life temperature of the copolymer or copolymer composition in the examples and comparative examples was measured with the apparatus and conditions shown in Table 1 below.

[0038]

Table 1

[0039] [Measurement of Initial Elastic Modulus] The methods for measuring the initial elastic modulus in Example 4 and Comparative Examples 1 and 2 are as follows. Test pieces were prepared from the depolymerizable copolymer compositions obtained in Example 4 and Comparative Examples 1 and 2 using a test piece punching machine, and a tensile test was conducted under the following apparatus and conditions. The measurement was performed three times, and the variation in the measured values was also examined. Apparatus: "LTS-1kNB-s50" manufactured by Minebea Tensile speed: 5 mm / min. Distance between chucks: 30 mm

[0040] [Synthesis Examples 1 to 6] Ion-exchanged water, sodium carbonate, and "KS Soap (solid content 90%)" manufactured by Kao Corporation were charged into a four-necked flask and dissolved while stirring. After dissolution, a monomer mixture (α-methylstyrene (AMS), methyl methacrylate (MMA)) was added, and the inside of the system was purged with argon gas while stirring at 150 rpm. When it was confirmed that the temperature inside the flask reached 3 to 4 °C, sodium nitrite, sodium iron(III) ethylenediaminetetraacetate trihydrate, tetrasodium ethylenediaminetetraacetate tetrahydrate, sodium formaldehyde sulfoxylate, and cumene hydroperoxide (pure content 80%) were sequentially added, and stirring was carried out for 63 hours while maintaining the temperature inside the flask at 3 to 4 °C. After stirring for 63 hours, 2,6-di-t-butyl-4-methylphenol was added to stop the reaction. The above reaction solution was dropped into methanol, and the precipitated white solid was recovered by filtration. The obtained white solid was simply dried, dissolved in tetrahydrofuran (THF), this solution was dropped into methanol, and the precipitated solid was recovered by filtration. The obtained white solid was dried under reduced pressure at 50 °C for 48 hours to obtain the final product. In the above synthesis procedure, the synthesis conditions shown in Table 2 were adopted to synthesize AMS / MMA copolymer polymers A to F, respectively.

[0041]

Table 2

[0042] [Example 1] When the monomer ratio of the AMS / MMA copolymer A obtained in Synthesis Example 1 was analyzed by NMR, it was found that AMS:MMA = 60:40 (molar ratio). Further, when the molecular weight of this AMS / MMA copolymer A was analyzed by GPC, the weight average molecular weight (Mw) was approximately 126,000. Furthermore, the obtained AMS / MMA copolymer was analyzed with a thermogravimetric differential thermal analyzer (TG-DTA) capable of observing images (N 2 environment, heating rate 10°C / min), and as a result, the decomposition start temperature was approximately 200°C, the decomposition end temperature was approximately 350°C, the decomposition rate was 100%, and no residue was observed. In addition, similar results were obtained in the thermogravimetric differential thermal analysis of the AMS / MMA copolymers B to F obtained in Synthesis Examples 2 to 6. 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 AMS / MMA copolymer did not show such discoloration associated with decomposition, and it was confirmed that it completely decomposed into monomers, indicating high depolymerization properties. When the half-life temperature of the AMS / MMA copolymer A was measured, it was 221°C. The AMS / MMA copolymer A was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, slowly dried, and then the appearance was observed. It was confirmed that a film was formed.

[0043] [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 to the AMS / MMA copolymer A at 5% by weight. After pouring it into a glass petri dish and slowly drying, the appearance was observed. It was confirmed that a film was formed. In addition, when measuring the half-life temperature of the AMS / MMA copolymer A composition after adding tris-2-ethylhexyl trimellitate, it was 198°C.

[0044] [Example 3] The AMS / MMA copolymer A obtained in Synthesis Example 1 was dissolved in tetrahydrofuran (THF), and tris-2-ethylhexyl trimellitate as a plasticizer was added to the AMS / MMA copolymer A so as to be 10% by weight. It was poured into a glass petri dish and slowly dried, and then the appearance was observed. As a result, it was confirmed that a film was formed. In addition, when measuring the half-life temperature of the AMS / MMA copolymer A composition after adding tris-2-ethylhexyl trimellitate, it was 182°C.

[0045] [Comparative Example 1] When analyzing the monomer ratio of the AMS / MMA copolymer B obtained in Synthesis Example 2 by NMR, it was AMS:MMA = 60:40 (molar ratio). In addition, when analyzing the molecular weight of this AMS / MMA copolymer B by GPC, the weight average molecular weight (Mw) was about 263,000. When measuring the half-life temperature of the AMS / MMA copolymer B, it was 245°C. When evaluating the fluidity at 245°C, decomposition of the resin was observed.

[0046] The AMS / MMA copolymer B was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. Then, when observing the appearance, it was confirmed that a film was formed. When measuring the initial elastic modulus of the AMS / MMA copolymer B, in three measurements, the initial elastic modulus showed stable values of 1700 to 2000 MPa.

[0047] [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 to the AMS / MMA copolymer B so as to be 10% by weight. It was poured into a glass petri dish and slowly dried, and when the appearance was observed, it was confirmed that a film was formed. Also, when the half-life temperature of the AMS / MMA copolymer B composition after adding tris-2-ethylhexyl trimellitate was measured, it was 195 °C. When the fluidity at 195 °C was evaluated, no resin decomposition was observed.. When the initial elastic modulus of the AMS / MMA copolymer B composition was measured, in three measurements, the initial elastic modulus showed stable values of 1900 - 2000 MPa, which were equivalent to those of Comparative Example 1.

[0048] [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 to the AMS / MMA copolymer B so as to be 20% by weight. It was poured into a glass petri dish and slowly dried, and when the appearance was observed, it was confirmed that a film was formed. Also, when the half-life temperature of the AMS / MMA copolymer B composition after adding tris-2-ethylhexyl trimellitate was measured, it was 185 °C. When the fluidity at 185 °C was evaluated, no resin decomposition was observed.. When the initial elastic modulus of the AMS / MMA copolymer B composition was measured, the initial elastic modulus showed large variations of 1500 - 2000 MPa in three measurements, indicating that a uniform resin composition could not be formed.

[0049] [Comparative Example 3] When the monomer ratio of the AMS / MMA copolymer C obtained in Synthesis Example 3 was analyzed by NMR, it was AMS:MMA = 65:35 (molar ratio). Also, when the molecular weight of this AMS / MMA copolymer C was analyzed by GPC, the weight average molecular weight (Mw) was approximately 28,000. When measuring the half-method temperature of the AMS / MMA copolymer C, it was 187°C. The AMS / MMA copolymer C was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. After observing the appearance, it was confirmed that there were cracks and the film could not be formed.

[0050] [Comparative Example 4] When analyzing the monomer ratio of the AMS / MMA copolymer D obtained in Synthesis Example 4 by NMR, it was AMS:MMA = 60:40 (molar ratio). Also, when analyzing the molecular weight of this AMS / MMA copolymer D by GPC, the weight average molecular weight (Mw) was approximately 34,000. When measuring the half-method temperature of the AMS / MMA copolymer D, it was 190°C. The AMS / MMA copolymer D was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. After observing the appearance, it was confirmed that there were cracks and the film could not be formed.

[0051] [Comparative Example 5] When analyzing the monomer ratio of the AMS / MMA copolymer E obtained in Synthesis Example 5 by NMR, it was AMS:MMA = 50:50 (molar ratio). Also, when analyzing the molecular weight of this AMS / MMA copolymer E by GPC, the weight average molecular weight (Mw) was approximately 26,000. When measuring the half-method temperature of the AMS / MMA copolymer E, it was 230°C. The AMS / MMA copolymer E was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. After observing the appearance, it was confirmed that there were cracks and the film could not be formed.

[0052] [Comparative Example 6] The AMS / MMA copolymer D obtained in Synthesis Example 4 was dissolved in tetrahydrofuran (THF), and tris-2-ethylhexyl trimellitate was added as a plasticizer to the AMS / MMA copolymer D at 10% by weight. It was poured into a glass petri dish and slowly dried. When the appearance was observed, cracks occurred and a film could not be formed. When the half-life temperature of the AMS / MMA copolymer D composition after the addition of tris-2-ethylhexyl trimellitate was measured, it was 154 °C.

[0053] [Comparative Example 7] The AMS / MMA copolymer D obtained in Synthesis Example 4 was dissolved in tetrahydrofuran (THF), and tris-2-ethylhexyl trimellitate was added as a plasticizer to the AMS / MMA copolymer D at 20% by weight. It was poured into a glass petri dish and slowly dried. When the appearance was observed, cracks occurred and a film could not be formed.

[0054] [Comparative Example 8] When the monomer ratio of the AMS / MMA copolymer F obtained in Synthesis Example 6 was analyzed by NMR, it was AMS:MMA = 60:40 (molar ratio). Also, when the molecular weight of this AMS / MMA copolymer F was analyzed by GPC, the weight average molecular weight (Mw) was about 51,000. When the half-life temperature of the AMS / MMA copolymer F was measured, it was 208 °C. The AMS / MMA copolymer F was dissolved in tetrahydrofuran (THF), poured into a glass petri dish, and slowly dried. When the appearance was observed, it was confirmed that there were cracks and a film could not be formed.

[0055] [Comparative Example 9] As an example of a polymer with low depolymerization property, TG-DTA analysis of polycarbonate (N 2As a result of performing the test under the environment with a heating 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, and it was observed that the decomposition proceeded to about 70%, but about 30% remained as a residue without being decomposed.

[0056] [Comparative Example 10] As an example of a polymer known to have depolymerizability, TG-DTA analysis of polymethyl methacrylate (N 2 As a result of performing the test under the environment with a heating rate of 10°C / min, the decomposition start temperature was about 300°C, and the decomposition end temperature was about 400°C, and it was observed that no residue remained.

[0057] The results of Examples 1 to 4 and Comparative Examples 1 to 10 are summarized in Table 3 below. In addition, Table 3 also shows the number average molecular weight (Mn) and dispersity (Mw / Mn) obtained during the measurement of the weight average molecular weight (Mw) of each AMS / MMA copolymer.

[0058] [Table 3]

[0059] [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 and had depolymerizability without residue in the TG-DTA analysis, with a decomposition start temperature of 200°C and a decomposition end temperature of 350°C, compared to Comparative Example 9. Comparing Comparative Example 10 with Examples 1 to 4 and Comparative Examples 1 to 8, it was confirmed that the Examples and Comparative Examples 1 to 8 decomposed at a lower temperature and had depolymerizability without residue in the TG-DTA analysis, with a decomposition start temperature of 200°C and a decomposition end temperature of 350°C, compared to Comparative Example 10.

[0060] Comparing Example 1 with Comparative Examples 1, 4, and 8, it can be seen 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 method temperature was 245°C, and it can be seen that the resin decomposed at the temperature showing good fluidity (=1 / 2 method temperature), making thermoforming difficult.

[0061] When Examples 1, 2, 3, Comparative Examples 1, 2 and Example 4 were compared, it was confirmed that the 1 / 2 method temperature could be reduced by adding a plasticizer. However, when 20% by weight of the plasticizer was added to the copolymer, the formed film did not show stable performance. Thus, it can be seen that the optimal amount of plasticizer added is 10% by weight or less based on the copolymer.

[0062] When Comparative Examples 3, 4 and 5 were compared, it was found that the higher the molar ratio of α-methylstyrene (AMS), the lower the 1 / 2 method temperature, and a copolymer with good fluidity at a lower temperature could be obtained. When AMS:MMA = 50:50, the 1 / 2 method temperature was as high as 230°C. At the temperature showing good fluidity (= 1 / 2 method temperature), the resin decomposed and thermoforming was difficult. Also, since AMS has low reactivity, to increase the AMS ratio, it is necessary to increase the charged amount of AMS. When AMS:MMA = 65:35, a large amount of AMS that did not react during synthesis increased. It was found that the AMS:MMA ratio with less unreacted AMS during the reaction and showing good fluidity was 60:40.

[0063] In Comparative Example 7, since it was difficult to form a film even when 20% by weight of the plasticizer was added to the copolymer, it can be seen that it is difficult to form a film even when a plasticizer is added to a copolymer with a low molecular weight.

Claims

1. A copolymer having 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 the weight average molecular weight is 70,000 to 300,000, and the copolymer has a depolymerizable copolymer with a half-life temperature measured by the method defined in JIS K7210-1 of 230°C or lower.

2. A copolymer composition comprising a copolymer having 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 the weight average molecular weight is 70,000 to 300,000, and a plasticizer, wherein the content of the plasticizer is 10% by weight or less based on the copolymer, and the copolymer composition is a depolymerizable copolymer composition having a half-life temperature measured by the method defined in JIS K7210-1 of 230°C or lower.

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

4. A resin molded article 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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