Method for preparing copolymer, copolymer prepared therefrom, and thermoplastic resin composition comprising the copolymer

Abstract

The present invention relates to a method for preparing a copolymer, a copolymer prepared by the method and a thermoplastic resin composition containing the copolymer, wherein the method comprises introducing an aromatic vinyl monomer, a vinyl nitrile monomer and an imide monomer and polymerizing them (S10), wherein the imide monomer is introduced at 1 wt % to 24 wt % at one time before the start of polymerization, and is continuously introduced at 76 wt % to 99 wt % from the start of polymerization.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0156419, filed with the Korean Intellectual Property Office on November 20, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0004] The present invention relates to a method for preparing a copolymer, and more particularly, to a method for preparing a heat-resistant copolymer using an aromatic vinyl monomer, a vinyl cyanide monomer, and an imide monomer, a copolymer prepared therefrom, and a thermoplastic resin composition containing the copolymer. Background Art

[0005] Generally, styrene copolymers have excellent moldability, rigidity, and electrical properties, and thus are widely used in various industrial fields, including OA devices and equipment such as computers, printers, and copiers, household appliances such as televisions and audio systems, electrical and electronic parts, automotive parts, sundries, etc.

[0006] Among them, in products that require heat resistance, such as automotive interior and exterior materials, a heat-resistant styrene copolymer and a diene graft copolymer such as an ABS resin are used in combination. Here, the heat-resistant styrene copolymer is prepared by adding a heat-resistant monomer such as an α-methylstyrene monomer or a maleimide monomer such as N-phenylmaleimide to increase heat resistance, and the maleimide monomer is particularly suitable for high heat-resistant products.

[0007] However, the maleimide monomer forms a charge transfer complex with an aromatic vinyl monomer such as styrene, thereby forming an alternating copolymer of the aromatic vinyl monomer and the maleimide monomer at the beginning of polymerization, and as the maleimide monomer is consumed, various changes occur in the composition of each monomer in the copolymer.

[0008] Specifically, the copolymer is prepared as a copolymer composition in which an alternating copolymer of an aromatic vinyl monomer and a maleimide monomer, a terpolymer of an aromatic vinyl monomer, a vinyl cyanide monomer, and a maleimide monomer, and a binary copolymer formed from an aromatic vinyl monomer and a vinyl cyanide monomer after the maleimide monomer is consumed are mixed with each other.

[0009] That is, when an aromatic vinyl monomer, a vinyl cyanide monomer, and a maleimide monomer are copolymerized, the monomer units are not uniformly formed in the copolymer, and a copolymer composition in which copolymers having different repeating units are mixed together is generated. Therefore, there is a problem in that the glass transition temperature of the copolymer is lowered.

[0010] In order to solve the above problems, a method of using continuous bulk polymerization or solution polymerization in preparing copolymers has been proposed. However, when these polymerization methods are used, it is difficult to control the polymerization temperature due to the heat of reaction, and the polymerization conversion rate is limited due to the increase in viscosity, so that unreacted monomers remain. Therefore, it is necessary to perform a separate process to recover the unreacted monomers.

[0011] In addition to the above methods, a method of using emulsion polymerization in preparing copolymers has been proposed. However, when using the emulsion polymerization method, unreacted monomers, polymerization additives, etc. remain in the polymer, causing the problem of coloration or discoloration of the copolymer, and after the slurry is prepared through a coagulation process after the polymerization reaction, the slurry is subjected to a post-treatment process of washing, dehydration, and drying, resulting in reduced production efficiency, equipment, and wastewater treatment problems.

[0012] [Prior art literature]

[0013] [Patent Document]

[0014] (Patent Document 1) JP3241815B2 Summary of the invention

[0015] Technical problem

[0016] One aspect of the present invention provides a method for preparing a copolymer, which can solve the heterogeneity of monomer units in the copolymer, minimize the formation of a copolymer composition obtained by mixing copolymers having different repeating units together, and thus prevent the glass transition temperature from decreasing.

[0017] Technical solution

[0018] According to one aspect of the present invention, a method for preparing a copolymer, a copolymer prepared thereby, and a thermoplastic resin composition including the copolymer are provided.

[0019] (1) The present invention provides a method for preparing a copolymer, which comprises introducing an aromatic vinyl monomer, a vinyl nitrile monomer and an imide monomer and polymerizing them (S10), wherein the imide monomer is introduced at 1 wt % to 24 wt % at one time before the start of the polymerization, and is continuously introduced at 76 wt % to 99 wt % from the start of the polymerization.

[0020] (2) In the above (1), the present invention provides a method for preparing a copolymer, wherein the entire amount of the aromatic vinyl-based monomer is introduced at once before the start of polymerization.

[0021] (3) In the above (1) or (2), the present invention provides a method for producing a copolymer, wherein the entire amount of the vinyl nitrile monomer is introduced at once before the start of polymerization.

[0022] (4) In any one of the above (1) to (3), the present invention provides a method for preparing a copolymer, wherein 1% to 24% by weight of the imide monomer is introduced at one time before the start of polymerization, and 76% to 99% by weight is continuously introduced from the time point when the temperature in the polymerization reactor reaches the polymerization temperature to the time point when the polymerization conversion rate is 60% to 80%.

[0023] (5) In any one of the above (1) to (4), the present invention provides a method for producing a copolymer, wherein the imide monomer continuously introduced from the start of polymerization is continuously introduced in divided portions at a constant rate.

[0024] (6) In any one of the above (1) to (5), the present invention provides a method for preparing a copolymer, wherein 10 wt% to 20 wt% of the imide monomer is introduced at once before the start of polymerization, and 80 wt% to 90 wt% is introduced after the start of polymerization.

[0025] (7) In any one of the above (1) to (6), the present invention provides a method for preparing a copolymer, wherein the amount of the introduced imide monomer is 31 wt% to 39 wt% based on the total content of the introduced monomers including aromatic vinyl monomers, vinyl nitrile monomers and imide monomers.

[0026] (8) In any one of the above (1) to (7), the present invention provides a method for preparing a copolymer, wherein the amount of the introduced imide monomer is 32 wt% to 36 wt% based on the total content of the introduced monomers including aromatic vinyl monomers, vinyl nitrile monomers and imide monomers.

[0027] (9) In any one of the above (1) to (8), the present invention provides a method for preparing a copolymer, wherein the polymerization in step S10 is performed by suspension polymerization.

[0028] (10) The present invention provides a copolymer comprising an aromatic vinyl monomer unit, a vinyl nitrile monomer unit and an imide monomer unit, wherein the glass transition temperature of the copolymer is above 178°C and the change in the glass transition temperature (ΔTg) calculated by the following formula 1 is below 15°C.

[0029] [Formula 1]

[0030] ΔTg (°C) = Max Tg (the highest value of the polymer glass transition temperature measured with the polymerization conversion rate during the polymerization of the copolymer) - Min Tg (the lowest value of the polymer glass transition temperature measured with the polymerization conversion rate during the polymerization of the copolymer)

[0031] (11) In the above (10), the present invention provides a copolymer, wherein the copolymer contains 1% to 20% by weight of vinyl cyanide monomer units, and the change amount (ΔAN) of the content of vinyl cyanide monomers calculated by the following formula 2 is 3% by weight or less.

[0032] [Formula 2]

[0033] ΔAN (% by weight) = Max AN (the highest value among the contents of vinyl cyanide monomers in the polymer measured with the polymerization conversion rate during the copolymerization) - Min AN (the lowest value among the contents of vinyl cyanide monomers in the polymer measured with the polymerization conversion rate during the copolymerization)

[0034] (12) The present invention provides a thermoplastic resin composition containing the copolymer described in the above (10) or (11) and a thermoplastic resin.

[0035] Advantageous effects

[0036] According to the method for preparing a copolymer of the present invention, a copolymer in which the non-uniformity of monomer units in the copolymer is solved can be prepared, and the generation of a copolymer composition obtained by mixing copolymers having different repeating units is minimized. Therefore, a decrease in the glass transition temperature is prevented. Detailed Description

[0037] Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

[0038] It should be understood that the words or terms used in the description and claims of the present invention should not be construed as being limited to the meanings defined in a common dictionary. It should be further understood that based on the principle that the inventor can appropriately define the meanings of words or terms to best explain the present invention, the words or terms should be construed as having meanings consistent with their meanings in the context of the related art and the technical concept of the present invention.

[0039] In the present invention, the term "monomer unit" may represent a component, structure, or material itself derived from a monomer, and as a specific example, it may represent a repeating unit formed in a polymer when the introduced monomer participates in a polymerization reaction during the polymerization of the polymer.

[0040] The term "derivative" used in the present invention may represent a compound having a structure in which one or more hydrogen atoms constituting the original compound are replaced by a halogen group, an alkyl group, or a hydroxyl group.

[0041] The term "composition" used in the present invention includes not only reaction products and decomposition products formed from the materials of the corresponding composition, but also mixtures containing the materials of the corresponding composition.

[0042] The present invention provides a method for preparing a copolymer. Specifically, the method for preparing the copolymer may be a method for preparing a heat-resistant copolymer by introducing an imide monomer. As a specific example, it may be a method for preparing a heat-resistant styrene copolymer.

[0043] According to an embodiment of the present invention, the method for preparing a polymer includes introducing an aromatic vinyl monomer, a vinyl cyanide monomer, and an imide monomer and polymerizing them (S10). Among them, 1% to 24% by weight of the imide monomer may be introduced at one time before the start of polymerization, and 76% to 99% by weight may be continuously introduced from the start of polymerization.

[0044] According to an embodiment of the present invention, the polymerization in step S10 may be carried out by suspension polymerization. The suspension polymerization method uses a water-soluble solvent such as water as a medium, so it has the advantages of easy reaction control even when the polymerization conversion rate is high, less use of additives, and a simple cleaning process. Generally, the suspension polymerization method is carried out by batch polymerization, and the reactants containing the monomers for polymerization are introduced into the reactor at one time before the start of polymerization. At this time, the maleimide monomer forms a charge transfer complex with an aromatic vinyl monomer such as styrene, so an alternating copolymer of the aromatic vinyl monomer and the maleimide monomer is formed at the start of polymerization. As the maleimide monomer is consumed, the composition of each monomer in the copolymer changes in various ways, resulting in a decrease in the heat resistance of the copolymer.

[0045] However, in the method for preparing a copolymer of the present invention, 1% to 24% by weight of the imide monomer is introduced at one time before the start of polymerization, and 76% to 99% by weight is introduced after the start of polymerization, so that the non-uniformity of the monomer units in the prepared copolymer can be solved, and the decrease in the glass transition temperature of the copolymer caused by the elapsed time of the polymerization reaction or the increase in the polymerization conversion rate can be prevented, thereby maintaining the glass transition temperature of the prepared copolymer at a relatively high level.

[0046] According to an embodiment of the present invention, the aromatic vinyl monomer may be one or more selected from the group consisting of styrene, α-methylstyrene, α-ethylstyrene, p-methylstyrene, o-methylstyrene, o-tert-butylstyrene, bromostyrene, chlorostyrene, trichlorostyrene, and their derivatives. As a specific example, it may be styrene.

[0047] According to one embodiment of the present invention, based on the total content of the introduced monomers including the aromatic vinyl monomers, the vinyl nitrile monomers and the imide monomers, the introduced amount of the aromatic vinyl monomers may be 30 wt % to 65 wt %, 40 wt % to 60 wt % or 45 wt % to 55 wt %, within which the following effects are achieved: a copolymer is obtained with a high polymerization conversion rate, and excellent compatibility with the thermoplastic resin is achieved while maintaining the mechanical properties of the copolymer. In addition, according to an embodiment of the present invention, the entire amount of the aromatic vinyl monomers may be introduced at once before the polymerization of step S10 is started.

[0048] According to one embodiment of the present invention, the vinyl nitrile monomer may be one or more selected from the group consisting of acrylonitrile, methacrylonitrile, ethacrylonitrile and derivatives thereof, and as a specific example, may be acrylonitrile.

[0049] In addition, according to one embodiment of the present invention, based on the total content of the introduced monomers including the aromatic vinyl monomers, the vinyl nitrile monomers and the imide monomers, the introduction amount of the vinyl nitrile monomers can be 1 wt % to 20 wt %, 5 wt % to 20 wt % or 5 wt % to 15 wt %, within which the following effects are achieved: a copolymer is obtained with a high polymerization conversion rate, excellent compatibility with the thermoplastic resin is achieved, and the mechanical properties of the copolymer are maintained. In addition, according to one embodiment of the present invention, the entire amount of the vinyl nitrile monomers can be introduced at once before the polymerization of step S10 is started.

[0050] According to one embodiment of the present invention, the imide monomer may be a maleimide monomer. As a specific example, the imide monomer may be a maleimide monomer in which the hydrogen bonded to the N atom of maleimide is replaced by a substituent. As a more specific example, the imide monomer can be one or more selected from the group consisting of N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide, N-cyclohexylmaleimide, N-chlorophenylmaleimide, N-methylphenylmaleimide, N-bromophenylmaleimide, N-laurylmaleimide, N-hydroxyphenylmaleimide, N-methoxyphenylmaleimide, N-carboxyphenylmaleimide, N-nitrophenylmaleimide, N-phenylmaleimide, 2-methyl-N-phenylmaleimide, N-benzylmaleimide, N-naphthylmaleimide and their derivatives, and as a specific example, it can be N-phenylmaleimide.

[0051] According to one embodiment of the present invention, based on the total content of the introduced monomers including aromatic vinyl monomers, vinyl nitrile monomers and imide monomers, the introduced amount of the imide monomers can be 31% to 39% by weight, 32% to 38% by weight or 32% to 36% by weight. Within this range, the following effects are achieved: a copolymer is obtained with a high polymerization conversion rate, a copolymer having a uniform monomer unit composition is prepared, and excellent heat resistance of the prepared copolymer is achieved. Here, the introduced amount of the imide monomers can be the sum of the imide monomers introduced once before the start of the polymerization in step S10 and the imide monomers introduced continuously after the start of the polymerization reaction in step S10.

[0052] According to one embodiment of the present invention, 1 wt% to 24 wt% of the imide monomers may be introduced at one time before the start of polymerization, and 76 wt% to 99 wt% of the imide monomers may be continuously introduced from the start of polymerization. Here, the weight % of the imide monomers refers to the weight % relative to the total amount of the imide monomers introduced during the polymerization process of step S10.

[0053] According to one embodiment of the present invention, continuous introduction may refer to a one-time continuous introduction of a certain amount according to the polymerization conversion rate, or may mean a continuous introduction of a certain amount at a constant speed. Constant speed may refer to the introduction speed of the imide monomer introduced by continuous segmentation, and as a specific example, may refer to a constant flow rate. That is, according to one embodiment of the present invention, 76% to 99% by weight of the imide monomer introduced after the start of polymerization may be continuously segmented and introduced at a constant speed, and as a specific example, may be introduced into the reaction system at a constant flow rate from the start of polymerization to the end of introduction. As described above, when 76% to 99% by weight of the imide monomer is continuously segmented and introduced at a constant speed, the difference in polymerization speed caused by the difference in reactivity between the monomers can be minimized, thereby having the effect of preparing a copolymer having a uniform monomer unit composition while maintaining a constant polymerization speed.

[0054] According to one embodiment of the present invention, 1 wt% to 24 wt% of the imide monomer can be introduced at one time before the start of polymerization, and 76 wt% to 99 wt% of the imide monomer can be continuously introduced from the time point when the temperature in the polymerization reactor reaches the polymerization temperature to the time point when the polymerization conversion rate is 60% to 80%. That is, the start of polymerization can refer to the time point when the temperature in the polymerization reactor reaches the polymerization temperature. In addition, the 76 wt% to 99 wt% of the imide monomer introduced after the start of polymerization can be introduced to the time point when the polymerization conversion rate is 60% to 80%, 65% to 80%, 70% to 80% or 75%, in which case the difference in polymerization rate caused by the difference in reactivity between the monomers can be minimized, thereby having the effect of preparing a copolymer with a uniform monomer unit composition while maintaining a constant polymerization rate.

[0055] According to one embodiment of the present invention, 1 wt% to 24 wt% of the imide monomer can be introduced at one time before the start of polymerization, and 76 wt% to 99 wt% of the imide monomer can be continuously introduced for 120 minutes to 240 minutes from the time point when the temperature in the polymerization reactor reaches the polymerization temperature. That is, the start of polymerization refers to the time point when the temperature in the polymerization reactor reaches the polymerization temperature. In addition, the 76 wt% to 99 wt% of the imide monomer introduced after the start of polymerization can be introduced for 120 minutes to 240 minutes, 150 minutes to 240 minutes, 180 minutes to 240 minutes or 210 minutes from the time point when the temperature in the polymerization reactor reaches the polymerization temperature. In this case, the difference in polymerization rate caused by the difference in reactivity between the monomers can be minimized, thereby having the effect of preparing a copolymer having a uniform monomer unit composition while maintaining a constant polymerization rate.

[0056] According to one embodiment of the present invention, 5 wt % to 20 wt % or 10 wt % to 20 wt % of the imide monomer can be introduced at one time before the start of polymerization, and 80 wt % to 95 wt % or 80 wt % to 90 wt % can be introduced after the start of polymerization. Within this range, the following effects are achieved: the heterogeneity of the monomer units in the copolymer is resolved, and the generation of a copolymer composition obtained by mixing copolymers with different repeating units is minimized, thereby preventing a decrease in the glass transition temperature.

[0057] According to one embodiment of the present invention, the method of preparing the copolymer may be performed by suspension polymerization, and thus, the polymerization may be performed in the presence of one or more additives selected from the group consisting of a water-soluble solvent, a polymerization initiator, a molecular weight controller, and a dispersant.

[0058] According to one embodiment of the present invention, the water-soluble solvent may be ion-exchanged water or deionized water.

[0059] According to one embodiment of the present invention, the polymerization initiator may be one or more selected from the group consisting of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, di(tert-butylperoxyisopropyl)benzene, tert-butylperoxyisopropylbenzene, di(tert-amyl)peroxide, dicumyl peroxide, butyl 4,4-di(tert-butylperoxy)valerate, tert-butyl peroxybenzoate, 2,2-di(tert-butylperoxy)butane, tert-amyl peroxybenzoate, tert-butyl peroxyacetate, tert-butylperoxy(2-ethylhexyl)carbonate, tert-butylperoxyisopropyl carbonate, tert-butyl peroxy-3,5,5-trimethylhexanoate, 1,1-bis(tert-butylperoxy)cyclohexane, tert-amyl peroxyacetate, tert-amylperoxy(2-ethylhexyl)carbonate, 1,1-di(tert-butylperoxy)-3,5,5-trimethylcyclohexane, 1,1-di(tert-amylperoxy)cyclohexane, tert-butyl monoperoxymaleate, 1,1'-azobis(hexahydrobenzonitrile), and 1,1'-azobis(cyclohexane-1-carbonitrile).

[0060] According to one embodiment of the present invention, based on 100 parts by weight of the total content of the introduced monomers, the polymerization initiator may be 0.01 to 1.00 parts by weight, 0.02 to 0.08 parts by weight, or 0.05 to 0.07 parts by weight, and within this range, there is an effect of achieving excellent polymerization stability.

[0061] According to one embodiment of the present invention, the molecular weight regulator may be one or more selected from the group consisting of α-methylstyrene dimer, tert-dodecyl mercaptan, n-dodecyl mercaptan, octyl mercaptan, carbon tetrachloride, dichloromethane, dibromomethane, tetraethylthiuram disulfide, dipentamethylenethiuram disulfide, and diisopropylxanthogen disulfide.

[0062] According to one embodiment of the present invention, based on 100 parts by weight of the total content of the introduced monomers, the molecular weight regulator may be 0.01 to 0.50 parts by weight, 0.10 to 0.40 parts by weight, or 0.10 to 0.30 parts by weight, and within this range, a copolymer having a suitable weight-average molecular weight can be prepared.

[0063] According to one embodiment of the present invention, the dispersant may be one or more selected from the group consisting of water-soluble polyvinyl alcohol, partially saponified polyvinyl alcohol, polyacrylic acid, copolymer of vinyl acetate and maleic anhydride, hydroxypropyl methylcellulose, gelatin, calcium phosphate, tricalcium phosphate, hydroxyapatite, sorbitan monolaurate, sorbitan trioleate, polyoxyethylene, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, and sodium dioctyl sulfosuccinate.

[0064] According to an embodiment of the present invention, based on 100 parts by weight of the total content of the introduced monomers, the dispersant can be 0.5 to 2.0 parts by weight, 0.5 to 1.5 parts by weight, or 1.0 to 1.5 parts by weight. Within this range, copolymers with more uniform particles can be prepared by improving the dispersion stability of the monomers in the polymerization system.

[0065] According to an embodiment of the present invention, the method for preparing the copolymer can be carried out by further including a co-dispersant. As a specific example, the co-dispersant can be a polyethylene oxide-based co-dispersant. As a more specific example, it can be polyethylene oxide alkyl ether phosphate. In this case, it has the effect of excellent polymerization stability.

[0066] According to an embodiment of the present invention, the method for preparing the copolymer can be carried out in a polymerization reactor equipped with a stirrer. Here, the stirrer can continuously apply a stirring force during the polymerization reaction. At this time, the stirring speed of the stirrer can be 100 RPM to 1000 RPM, 300 RPM to 800 RPM, or 400 RPM to 600 RPM. And within this range, copolymers with more uniform particles can be prepared by improving the dispersion stability of the monomers in the polymerization system.

[0067] According to an embodiment of the present invention, the polymerization in step S10 can be carried out by raising the temperature two or more times. Here, raising the temperature means increasing the temperature inside the reactor where the polymerization reaction is carried out. Raising the temperature two or more times means further raising the temperature one or more times during the polymerization reaction (including the time point when the initial temperature is reached and after the initial temperature is reached). As described above, when the polymerization is carried out by raising the temperature two or more times, it is easy to control the reaction heat and prevent the explosive occurrence of the polymerization reaction. Thus, the polymerization reaction can be carried out under mild conditions. Then, by further raising the temperature one or more times, the effect of improving the polymerization conversion rate can be achieved.

[0068] According to an embodiment of the present invention, when the polymerization in step S10 is carried out by raising the temperature two or more times, the temperature inside the reactor at the time point when the initial temperature is reached can be 80°C to 95°C, 85°C to 95°C, or 90°C to 95°C. Within this range, it has the effect of achieving excellent polymerization stability.

[0069] According to an embodiment of the present invention, when the polymerization in step S10 is carried out by raising the temperature two or more times, when raising the temperature one or more times after the initial temperature is reached, the temperature inside the reactor after the temperature rise can be 100°C to 130°C, 110°C to 130°C, or 115°C to 125°C. Within this range, it has the effect of preparing the copolymer with a high polymerization conversion rate.

[0070] According to an embodiment of the present invention, the polymerization in step S10 may be carried out until the polymerization conversion rate is 90% or more, or 90% to 100%.

[0071] As described above, when preparing a copolymer by the method for preparing a copolymer of the present invention, the non-uniformity of monomer units in the copolymer can be solved, the polymerization reaction can be maintained at a high polymerization conversion rate, and the decrease in the glass transition temperature can be prevented, thereby preparing a copolymer with excellent heat resistance.

[0072] In addition, the present invention provides a copolymer prepared by the method for preparing a copolymer. Specifically, the copolymer may be a heat-resistant copolymer containing imide monomer units, and as a more specific example, it may be a heat-resistant styrene copolymer.

[0073] According to an embodiment of the present invention, the copolymer may contain aromatic vinyl monomer units, vinyl cyanide monomer units, and imide monomer units, its glass transition temperature may be 178 °C or more, and the change amount of the glass transition temperature (ΔTg) calculated by the following formula 1 may be 15 °C or less.

[0074] [Formula 1]

[0075] ΔTg (°C) = Max Tg (the highest value among the polymer glass transition temperatures measured with the polymerization conversion rate during the copolymer polymerization) - Min Tg (the lowest value among the polymer glass transition temperatures measured with the polymerization conversion rate during the copolymer polymerization)

[0076] According to an embodiment of the present invention, the glass transition temperature of the copolymer may be 178 °C or more, 178 °C to 190 °C, 179 °C to 185 °C, or 179 °C to 181 °C. As described above, the copolymer of the present invention has a high glass transition temperature, and thus has the effect of excellent heat resistance.

[0077] According to an embodiment of the present invention, the aromatic vinyl monomer units, vinyl cyanide monomer units, and imide monomer units may respectively refer to repeating units formed due to the participation of aromatic vinyl monomers, vinyl cyanide monomers, and imide monomers in the polymerization reaction. As a specific example, the polymerization reaction may be a radical polymerization reaction. Therefore, the aromatic vinyl monomer units, vinyl cyanide monomer units, and imide monomer units may respectively refer to repeating units derived from the carbon-carbon double bonds present in the aromatic vinyl monomers, vinyl cyanide monomers, and imide monomers.

[0078] According to one embodiment of the present invention, the copolymer may be a random copolymer, and the composition of the aromatic vinyl monomer unit, vinyl cyanide monomer unit, and imide monomer unit in the copolymer may be uniform. When the composition of the monomer units is uniform, this may mean that the ratio of each monomer unit in the polymer polymerized and grown through the polymerization reaction of the monomers remains uniform. As a specific example, this may mean that as the polymerization proceeds, when a part of the polymer in the reactor is collected at each polymerization conversion rate during the polymerization, the ratio of each monomer unit forming the corresponding polymer remains uniform.

[0079] The present invention calculates and represents the uniformity of the monomer unit composition by ΔTg calculated by the above formula 1.

[0080] ΔTg calculated by the above formula 1 represents the difference between the highest value and the lowest value of the glass transition temperature of the polymer measured with the polymerization conversion rate during the polymerization of the copolymer. As the polymerization proceeds, when a part of the polymer in the reactor is collected at each polymerization conversion rate during the polymerization, the glass transition temperature of each polymer is determined by the ratio of each monomer unit forming the corresponding polymer. Therefore, it can be seen that the smaller the difference in the glass transition temperature of the copolymer (i.e., the polymer) at each polymerization conversion rate, the more uniform the ratio of each monomer unit in the copolymer (i.e., the polymer) at each polymerization conversion rate is maintained.

[0081] According to one embodiment of the present invention, ΔTg of the copolymer calculated by the above formula 1 may be 15 °C or less, 0.1 °C to 15 °C, 0.1 °C to 10 °C, 0.1 °C to 5 °C, or 0.9 °C to 2.7 °C. Within this range, the composition of each monomer unit in the copolymer is uniform, thereby having the effect of improving the glass transition temperature and thus having excellent heat resistance.

[0082] According to one embodiment of the present invention, ΔTg of each polymer calculated by the above formula 1 can be calculated based on the glass transition temperature measured for the polymers at the time points of polymerization conversion rates of 10%, 30%, 50%, 70%, and 90%.

[0083] According to one embodiment of the present invention, the copolymer contains 1% by weight to 20% by weight of vinyl cyanide monomer units, and the content change amount (ΔAN) of vinyl cyanide monomers calculated by the following formula 2 may be 3% by weight or less.

[0084] [Formula 2]

[0085] ΔAN (% by weight) = Max AN (the highest value of the vinyl cyanide monomer content in the polymer measured with the polymerization conversion rate during the polymerization of the copolymer) - Min AN (the lowest value of the vinyl cyanide monomer content in the polymer measured with the polymerization conversion rate during the polymerization of the copolymer)

[0086] According to an embodiment of the present invention, the above copolymer may contain 1% to 20% by weight, 5% to 20% by weight, 5% to 15% by weight, or 8% to 10% by weight of vinyl cyanide monomer units. This is the content of vinyl cyanide monomer units present in the copolymer obtained after the completion of polymerization, and depends on the final polymerization conversion rate and the degree of participation of vinyl cyanide monomers in the polymerization reaction, and may differ from the content of vinyl cyanide monomers introduced in the preparation method of the above copolymer.

[0087] The present invention calculates and represents the homogeneity of the monomer unit composition by ΔAN calculated by the above formula (2).

[0088] ΔAN calculated by the above formula (2) represents the difference between the highest value and the lowest value of the content of vinyl cyanide monomer units in the polymer measured with the polymerization conversion rate during the copolymerization. As the polymerization proceeds, when a part of the polymer in the reactor is collected at each polymerization conversion rate during the polymerization process, the content of vinyl cyanide monomer units in each polymer is determined by the ratio of each monomer unit forming the corresponding polymer. Therefore, it can be seen that the smaller the difference in the content of vinyl cyanide monomer units in the copolymer (i.e., the polymer) at each polymerization conversion rate, the more uniform the ratio of each monomer unit in the copolymer (i.e., the polymer) is maintained at each polymerization conversion rate.

[0089] According to an embodiment of the present invention, ΔAN of the copolymer calculated by the above formula (2) may be 3.0% by weight or less, 2.5% by weight or less, 2.0% by weight, 1.5% by weight, 0.1% to 1.5% by weight, 0.5% to 1.5% by weight, or 0.9% to 1.2% by weight. Within this range, the composition of each monomer unit in the copolymer is uniform, and thus has the effect of being able to increase the glass transition temperature and thus having excellent heat resistance.

[0090] According to an embodiment of the present invention, ΔAN of each polymer calculated by the above formula (2) can be calculated based on the content of vinyl cyanide monomer units in the copolymer measured from the polymers at the time points of polymerization conversion rates of 10%, 30%, 50%, 70%, and 90%.

[0091] In addition, the present invention provides a resin composition containing the copolymer. Specifically, the resin composition may be a thermoplastic resin composition containing the above copolymer and a thermoplastic resin. As a specific example, the thermoplastic resin composition may contain a copolymer and a diene graft copolymer.

[0092] According to an embodiment of the present invention, the diene graft copolymer may be an acrylonitrile-butadiene-styrene copolymer, which is used to provide excellent moldability and impact resistance to the thermoplastic resin composition, or may be a core-shell graft copolymer including a core having a conjugated diene monomer unit and a shell surrounding the core and having an aromatic vinyl monomer unit and a vinyl cyanide monomer unit.

[0093] According to an embodiment of the present invention, the aromatic vinyl monomer of the diene graft copolymer may be one or more selected from the group consisting of styrene, α-methylstyrene, α-ethylstyrene, p-methylstyrene, o-methylstyrene, o-tert-butylstyrene, bromostyrene, chlorostyrene, trichlorostyrene, and their derivatives. As a specific example, it may be styrene.

[0094] According to an embodiment of the present invention, the vinyl cyanide monomer of the diene graft copolymer may be one or more selected from the group consisting of acrylonitrile, methacrylonitrile, ethylacrylonitrile, and their derivatives. As a specific example, it may be acrylonitrile.

[0095] According to an embodiment of the present invention, the conjugated diene monomer of the diene graft copolymer may be one or more selected from the group consisting of 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and isoprene. As a specific example, it may be 1,3-butadiene.

[0096] According to an embodiment of the present invention, the acrylonitrile-butadiene-styrene copolymer may be prepared by emulsion polymerization and emulsion graft polymerization. For example, a core (or seed) as a rubber-like polymer may be prepared by emulsion polymerization of a conjugated diene monomer, and then a vinyl cyanide monomer and an aromatic vinyl monomer may be added to the core, followed by emulsion graft polymerization.

[0097] According to an embodiment of the present invention, the acrylonitrile-butadiene-styrene copolymer may include 30% to 70% by weight of a core having a conjugated diene monomer unit and 30% to 70% by weight of a shell surrounding the core and having an aromatic vinyl monomer unit and a vinyl cyanide monomer unit. At this time, the shell may contain the aromatic vinyl monomer unit and the vinyl cyanide monomer unit in a weight ratio of 7:3 to 8:2. In this case, the impact resistance, mechanical properties, and moldability of the copolymer may be more excellent.

[0098] When necessary, the thermoplastic resin composition according to an embodiment of the present invention may further contain one or more selected from the group consisting of an impact modifier, a lubricant, a heat stabilizer, an anti-dripping agent, an antioxidant, a light stabilizer, a light-shielding agent, a pigment, and an inorganic filler. In this case, based on 100 parts by weight of the copolymer and the thermoplastic resin, the amount of the additive may be 5.0 parts by weight or less, or 0.1 part by weight to 1.0 part by weight.

[0099] According to an embodiment of the present invention, there is no particular limitation on the specific materials of the additives that can be used as long as they are used in the thermoplastic resin composition. However, for example, as the anti-dripping agent, one or more selected from the group consisting of polytetrafluoroethylene (Teflon), polyamide, polysiloxane, polytetrafluoroethylene (PTFE), and tetrafluoroethylene-hexafluoropropylene (TFE-HFP) copolymer can be used to further improve the flame retardancy. As the inorganic filler, one or more selected from the group consisting of barium sulfate, barium glass filler, and barium oxide can be used.

[0100] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0101] Examples

[0102] Example 1

[0103] 140 parts by weight of ion-exchanged water, 48 parts by weight of styrene, 12 parts by weight of acrylonitrile, 4 parts by weight of N-phenylmaleimide, 0.05 part by weight of 1,1-bis(tert-butylperoxy)cyclohexane and 0.01 part by weight of tert-butyl peroxybenzoate as polymerization initiators, 1.3 parts by weight of tricalcium phosphate as a dispersant, and 0.2 part by weight of tert-dodecyl mercaptan as a molecular weight controller were introduced into a polymerization reactor equipped with a stirrer at one time. While the stirrer was operating at 500 RPM, the temperature was raised to 90°C to start the polymerization. From the time point when the temperature in the reactor reached 90°C, 36 parts by weight of N-phenylmaleimide was continuously introduced over 210 minutes while maintaining the same introduction rate to carry out the polymerization. When the continuous introduction of N-phenylmaleimide was completed, the polymerization conversion rate was 74.7%. Polymerization was carried out for 240 minutes from the time point when the temperature in the reactor reached 90°C, and then the temperature in the reactor was raised to 120°C and further polymerized for 120 minutes. After the polymerization was carried out for a total of 360 minutes, it was ended. At this time, the final polymerization conversion rate was 98.6%. Thereafter, formic acid was introduced into the polymerized slurry, and the pH of the slurry was adjusted to 2.5 to remove the dispersant, and then it was washed, dehydrated, and dried to prepare a bead copolymer.

[0104] Here, each part by weight is based on 100 parts by weight of the total introduced amount of monomers.

[0105] Example 2

[0106] The same operations were carried out in the same manner as in Example 1, except that in Example 1, before polymerization, the introduced amount of N-phenylmaleimide was 6 parts by weight instead of 4 parts by weight, and from the time point when the temperature in the reactor reached 90 °C, while maintaining the same introduction rate, 34 parts by weight instead of 36 parts by weight of N-phenylmaleimide was continuously introduced over 210 minutes for polymerization. When the continuous introduction of N-phenylmaleimide ended, the polymerization conversion rate was 75.0%, and the final polymerization conversion rate was 98.7%.

[0107] Example 3

[0108] The same operations were carried out in the same manner as in Example 1, except that in Example 1, before polymerization, the introduced amount of N-phenylmaleimide was 8 parts by weight instead of 4 parts by weight, and from the time point when the temperature in the reactor reached 90 °C, while maintaining the same introduction rate, 32 parts by weight instead of 36 parts by weight of N-phenylmaleimide was continuously introduced over 210 minutes for polymerization. When the continuous introduction of N-phenylmaleimide ended, the polymerization conversion rate was 75.2%, and the final polymerization conversion rate was 98.5%.

[0109] Comparative Example 1

[0110] The same operations were carried out in the same manner as in Example 1, except that in Example 1, N-phenylmaleimide was not introduced before polymerization, and from the time point when the temperature in the reactor reached 90 °C, while maintaining the same introduction rate, 40 parts by weight of N-phenylmaleimide was continuously introduced over 210 minutes for polymerization. When the continuous introduction of N-phenylmaleimide ended, the polymerization conversion rate was 74.6%, and the final polymerization conversion rate was 98.4%.

[0111] Comparative Example 2

[0112] The same operations were carried out in the same manner as in Example 1, except that in Example 1, before polymerization, the introduced amount of N-phenylmaleimide was 10 parts by weight instead of 4 parts by weight, and from the time point when the temperature in the reactor reached 90 °C, while maintaining the same introduction rate, 30 parts by weight instead of 36 parts by weight of N-phenylmaleimide was continuously introduced over 210 minutes for polymerization. When the continuous introduction of N-phenylmaleimide ended, the polymerization conversion rate was 75.2%, and the final polymerization conversion rate was 98.5%.

[0113] Comparative Example 3

[0114] The same operation was carried out in the same manner as in Example 1, except that in Example 1, before polymerization, the amount of N-phenylmaleimide introduced was 20 parts by weight instead of 4 parts by weight, and from the time point when the temperature in the reactor reached 90 °C, 20 parts by weight instead of 36 parts by weight of N-phenylmaleimide was continuously introduced over 210 minutes while maintaining the same introduction rate, and polymerization was carried out. When the continuous introduction of N-phenylmaleimide ended, the polymerization conversion rate was 75.4%, and the final polymerization conversion rate was 98.6%.

[0115] Comparative Example 4

[0116] The same operation was carried out in the same manner as in Example 1, except that in Example 1, before polymerization, the amount of N-phenylmaleimide introduced was 30 parts by weight instead of 4 parts by weight, and from the time point when the temperature in the reactor reached 90 °C, 10 parts by weight instead of 36 parts by weight of N-phenylmaleimide was continuously introduced over 210 minutes while maintaining the same introduction rate, and polymerization was carried out. When the continuous introduction of N-phenylmaleimide ended, the polymerization conversion rate was 76.4%, and the final polymerization conversion rate was 98.4%.

[0117] Comparative Example 5

[0118] The same operation was carried out in the same manner as in Example 1, except that in Example 1, before polymerization, the amount of N-phenylmaleimide introduced was 40 parts by weight instead of 4 parts by weight, and when polymerization was carried out from the time point when the temperature in the reactor reached 90 °C, no additional N-phenylmaleimide was introduced. The final polymerization conversion rate was 98.5%.

[0119] Comparative Example 6

[0120] 140 parts by weight of ion-exchanged water, 0.05 part by weight of 1,1-bis(tert-butylperoxy)cyclohexane and 0.01 part by weight of tert-butyl peroxybenzoate as polymerization initiators, 1.3 parts by weight of tricalcium phosphate as a dispersant, and 0.2 part by weight of tert-dodecyl mercaptan as a molecular weight controller were introduced all at once into a polymerization reactor equipped with a stirrer. While the stirrer was operating at 500 RPM, the temperature was raised to 90°C. Starting from the time point when the temperature inside the reactor reached 90°C, 48 parts by weight of styrene, 12 parts by weight of acrylonitrile, and 40 parts by weight of N-phenylmaleimide were continuously introduced over 210 minutes while maintaining the same introduction rate, and polymerization was carried out. When the continuous introduction of styrene, acrylonitrile, and N-phenylmaleimide was completed, the polymerization conversion rate was 74.8%. Polymerization was carried out for 240 minutes starting from the time point when the temperature inside the reactor reached 90°C, then the temperature inside the reactor was raised to 120°C, and polymerization was further carried out for 120 minutes. Polymerization was carried out for a total of 360 minutes and then ended. At this time, the final polymerization conversion rate was 98.4%. Thereafter, formic acid was introduced into the polymerized slurry, the pH of the slurry was adjusted to 2.5 to remove the dispersant, and then washing, dehydration, and drying were carried out to prepare a bead copolymer.

[0121] Here, each part by weight is based on 100 parts by weight of the total amount of monomers introduced.

[0122] Comparative Example 7

[0123] 140 parts by weight of ion-exchanged water, 48 parts by weight of styrene, 12 parts by weight of acrylonitrile, 4 parts by weight of N-phenylmaleimide, 0.05 part by weight of 1,1-bis(tert-butylperoxy)cyclohexane and 0.01 part by weight of tert-butyl peroxybenzoate as polymerization initiators, 1.3 parts by weight of tricalcium phosphate as a dispersant, and 0.2 part by weight of tert-dodecyl mercaptan as a molecular weight controller were introduced all at once into a polymerization reactor equipped with a stirrer. While the stirrer was operating at 500 RPM, the temperature was raised to 90°C to initiate polymerization. Starting from the time point when the polymerization conversion rate reached 30% (40 minutes after the time point when the temperature inside the reactor reached 90°C), 36 parts by weight of N-phenylmaleimide were continuously introduced while maintaining the same introduction rate, and polymerization was carried out. When the continuous introduction of N-phenylmaleimide was completed, the polymerization conversion rate was 76.0%. Polymerization was carried out for 240 minutes starting from the time point when the temperature inside the reactor reached 90°C, then the temperature inside the reactor was raised to 120°C, and polymerization was further carried out for 120 minutes. Polymerization was carried out for a total of 360 minutes and then ended. At this time, the final polymerization conversion rate was 98.5%. Thereafter, formic acid was introduced into the polymerized slurry, the pH of the slurry was adjusted to 2.5 to remove the dispersant, and then washing, dehydration, and drying were carried out to prepare a bead copolymer.

[0124] Here, each part by weight is based on 100 parts by weight of the total introduced amount of monomers.

[0125] Experimental Example

[0126] When preparing the copolymers of Preparation Examples 1 to 3 and Comparative Examples 1 to 7, the introduction timing and content of each monomer were measured respectively, and the content of vinyl cyanide monomer units in the copolymers and the glass transition temperature were measured when the polymerization conversion rates were 15%, 30%, 50%, 70% and 90%. The change amount of the glass transition temperature (ΔTg) was calculated by the following formula 1, and the change amount of the content of vinyl cyanide monomers (ΔAN) was calculated by the following formula 2, and are shown in Tables 1 to 3 below.

[0127] [Formula 1]

[0128] ΔTg (°C) = Max Tg (the highest value among the polymer glass transition temperatures measured with the polymerization conversion rate during the copolymer polymerization) - Min Tg (the lowest value among the polymer glass transition temperatures measured with the polymerization conversion rate during the copolymer polymerization)

[0129] [Formula 2]

[0130] ΔAN (wt%) = Max AN (the highest value among the vinyl cyanide monomer contents in the polymer measured with the polymerization conversion rate during the copolymer polymerization) - Min AN (the lowest value among the vinyl cyanide monomer contents in the polymer measured with the polymerization conversion rate during the copolymer polymerization)

[0131] * Polymerization conversion rate (%): When preparing the copolymers of the preparation examples and comparative examples, 4 g of polymer sample was collected and completely dissolved in tetrahydrofuran (THF). Then, methanol (MeOH) was introduced to obtain a precipitate, and the obtained precipitate was dried in vacuo to completely remove the solvent, thereby obtaining a dried polymer. The weight of the measured dried polymer was used to calculate the polymerization conversion rate by the following formula 3.

[0132] [Formula 3]

[0133] Polymerization conversion rate (%) = [(weight of dried polymer) / (total weight of monomers introduced when preparing 4 g of polymer)] × 100

[0134] * Content of vinyl cyanide monomer units in the copolymer (wt%): When preparing the copolymers of the preparation examples and comparative examples, for each polymerization conversion rate, 4 g of samples were collected from the polymers and copolymers, and then the samples were dried in a vacuum oven at 220 °C for 2 hours, and the content of vinyl cyanide monomer units in the copolymers was measured by elemental analysis using an elemental analyzer (Thermo Corporation, Flash 2000 elemental analyzer) under the following analysis conditions.

[0135] - Temperature of the CHNS reactor: 900 °C

[0136] - Temperature of the oxygen reactor: 1060 °C

[0137] - Temperature of the GC oven: 65 °C

[0138] - Flow rate of helium carrier gas: 140 ml / min for CHNS and 100 ml / min for oxygen

[0139] - Flow rate of helium reference gas: 100 ml / min

[0140] - Flow rate of oxygen: 250 ml / min for CHNS

[0141] - Oxygen injection time: 5 seconds for CHNS

[0142] - Sampling delay: 12 seconds for CHNS and 0 seconds for oxygen

[0143] - Total running time: 720 seconds for CHNS and 500 seconds for oxygen

[0144] * Glass transition temperature (Tg, °C): When preparing the copolymers of the preparation examples and comparative examples, for each polymerization conversion rate, a 0.01 g sample was collected from the polymers and copolymers, and then using a differential scanning calorimeter (DSC: TA instrument), the sample was first heated from room temperature (20 °C - 25 °C) to 250 °C to remove foreign substances, then the sample was cooled to room temperature (20 °C - 25 °C), and then heated for the second time to 250 °C, thereby determining the glass transition temperature.

[0145] [Table 1]

[0146]

[0147] [Table 2]

[0148]

[0149] [Table 3]

[0150]

[0151] As shown in Tables 1 to 3, it has been confirmed that the copolymers prepared by the method for preparing a copolymer of the present invention all exhibit a high glass transition temperature, and during the polymerization process, the content of vinyl cyanide monomer units in the copolymer and the glass transition temperature are maintained at similar levels without large deviations. In particular, it was confirmed that according to the results of ΔAN, the deviation of the content of vinyl cyanide monomer units in the copolymer at each polymerization conversion rate is very small, and according to the results of ΔTg, the deviation of the glass transition temperature of the copolymer at each polymerization conversion rate is very small. From the above results, it has been confirmed that in the copolymers of Examples 1 to 3 prepared according to the method for preparing a copolymer, the monomer units in the copolymer are uniformly formed, while minimizing the product obtained by mixing an alternating copolymer of an aromatic vinyl monomer and a maleimide monomer, a terpolymer of an aromatic vinyl monomer, a vinyl cyanide monomer and a maleimide monomer, and a binary copolymer formed by an aromatic vinyl monomer and a vinyl cyanide monomer after consumption of the maleimide monomer.

[0152] In contrast, in the case of Comparative Example 1 in which all the imide monomers were continuously introduced after the start of polymerization, the vinyl cyanide monomer participated in the polymerization reaction at a high ratio at the start of polymerization, but as the imide monomer was introduced, the participation rate gradually decreased, thus confirming that ΔAN increased sharply and ΔTg was also high, which confirmed that the composition of the monomer units in the copolymer was very non-uniform.

[0153] In addition, in the cases of Comparative Examples 2 and 3 in which the content of the imide monomer introduced before the start of polymerization and the content of the imide monomer continuously introduced after the start of polymerization were adjusted to a range close to the range defined in the present invention, the deviations of ΔAN and ΔTg were slightly reduced compared to Comparative Example 1, but did not reach a sufficient level.

[0154] In addition, in the case of Comparative Example 4 in which 75% by weight of the imide monomer was introduced before the start of polymerization and in the case of Comparative Example 5 in which all the imide monomers were introduced before the start of polymerization, when the temperature was raised to start polymerization, the polymerization had already proceeded rapidly. As the polymerization proceeded, only the vinyl cyanide monomer remained to continue the polymerization reaction. Therefore, as the polymerization proceeded, the glass transition temperature decreased significantly. Therefore, it was confirmed that ΔAN increased and ΔTg was also very high.

[0155] In addition, in the case of Comparative Example 6 in which all the aromatic vinyl monomers, vinyl cyanide monomer units and imide monomers were continuously introduced, the vinyl cyanide monomer did not participate in the polymerization reaction at the start of polymerization, but as the polymerization proceeded to the end, only the vinyl cyanide monomer remained to continue the polymerization reaction. Therefore, as the polymerization proceeded, the glass transition temperature decreased significantly. Therefore, it was confirmed that ΔAN increased and ΔTg was also very high.

[0156] In addition, in the case of Comparative Example 7 in which the imide monomer was introduced not from the start of polymerization but from the time point when the polymerization conversion reached 30%, it was confirmed that both ΔAN and ΔTg were higher than those in Example 1 in which the same amount of the imide monomer was introduced from the start of polymerization.

[0157] From the above results, it was confirmed that the method for preparing a copolymer according to the present invention can prepare a copolymer in which the non-uniformity of the monomer units in the copolymer is solved, minimize the formation of a copolymer composition obtained by mixing copolymers having different repeating units, and thus prevent the decrease in the glass transition temperature.

Claims

1. A method for preparing a copolymer, the method comprising: include: introducing an aromatic vinyl monomer, a vinyl nitrile monomer and an imide monomer and polymerizing them (S10), The imide monomer is introduced at 1 wt% to 24 wt% at one time before the start of polymerization, and is continuously introduced at 76 wt% to 99 wt% from the start of polymerization. wherein the entire amount of the aromatic vinyl monomer is introduced at once before the start of polymerization, wherein the entire amount of the vinyl nitrile monomer is introduced at once before the start of polymerization, and Wherein, the polymerization in step S10 is performed by suspension polymerization.

2. The method according to claim 1, in, The imide monomer is introduced at a time of 1 wt% to 24 wt% before the start of polymerization, and is continuously introduced at 76 wt% to 99 wt% from the time when the temperature in the polymerization reactor reaches the polymerization temperature to the time when the polymerization conversion rate is 60% to 80%.

3. The method according to claim 1, in, The imide monomer which is continuously introduced from the start of polymerization is continuously introduced in divided portions at a constant rate.

4. The method according to claim 1, in, The imide monomer is introduced at a time of 10 to 20% by weight before the start of polymerization, and 80 to 90% by weight is introduced after the start of polymerization.

5. The method according to claim 1, in, The introduced amount of the imide-based monomer is 31 wt % to 39 wt % based on the total content of the introduced monomers including the aromatic vinyl-based monomer, the vinyl nitrile-based monomer, and the imide-based monomer.

6. The method according to claim 1, in, The introduced amount of the imide-based monomer is 32 wt % to 36 wt % based on the total content of the introduced monomers including the aromatic vinyl-based monomer, the vinyl nitrile-based monomer, and the imide-based monomer.

7. A copolymer prepared by the method of claim 1, comprising: Aromatic vinyl monomer units; vinyl nitrile monomer units; and imide monomer units, in, The glass transition temperature of the copolymer is 178°C or higher, and the change in glass transition temperature (ΔTg) calculated by the following formula 1 is 15°C or lower; [Formula 1] △Tg (℃) = Max Tg (the highest value of the polymer glass transition temperature measured with the polymerization conversion rate during the polymerization of the copolymer) - Min Tg (the lowest value of the polymer glass transition temperature measured with the polymerization conversion rate during the polymerization of the copolymer) The ΔTg is calculated based on the glass transition temperature of the polymer measured at the time points when the polymerization conversion rate is 15%, 30%, 50%, 70% and 90%. The glass transition temperature is determined as follows: when preparing the copolymer, for each polymerization conversion rate, 0.01 g of sample is collected from the copolymer, and then a differential scanning calorimeter is used to heat the sample from a room temperature of 20°C to 25°C to 250°C for the first time to remove foreign matter, and then the sample is cooled to room temperature and heated to 250°C for a second time, thereby determining the glass transition temperature.

8. The copolymer according to claim 7, in, The copolymer contains 1% to 20% by weight of the vinyl cyanide monomer units, and the change amount (ΔAN) of the content of the vinyl cyanide monomer calculated by the following formula 2 is 3% by weight or less; [Formula 2] ΔAN (wt%) = Max AN (the highest value of the vinyl cyanide monomer content in the polymer measured according to the polymerization conversion rate during the copolymerization) - Min AN (the lowest value of the vinyl cyanide monomer content in the polymer measured according to the polymerization conversion rate during the copolymerization) wherein, the ΔAN is calculated based on the content of the vinyl cyanide monomer units in the copolymer measured from the polymers at the time points of polymerization conversion rates of 15%, 30%, 50%, 70% and 90%; wherein, the content of the vinyl cyanide monomer units in the copolymer is measured as follows: when preparing the copolymer, for each polymerization conversion rate, 4 g of the sample is collected from the copolymer, then the sample is dried in a vacuum oven at 220 °C for 2 hours, and the content of the vinyl cyanide monomer units in the copolymer is measured by elemental analysis using an elemental analyzer under the following analysis conditions: - CHNS reactor temperature: 900 °C - Oxygen reactor temperature: 1060 °C - GC oven temperature: 65 °C - Helium carrier gas flow rate: 140 ml / min for CHNS and 100 ml / min for oxygen - Helium reference flow rate: 100 ml / min - Oxygen flow rate: 250 ml / min for CHNS - Oxygen injection time: 5 seconds for CHNS - Sampling delay: 12 seconds for CHNS and 0 seconds for oxygen - Total running time: 720 seconds for CHNS and 500 seconds for oxygen.

9. A thermoplastic resin composition comprising the copolymer according to claim 7 and a thermoplastic resin.

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