PROCESS FOR PRODUCING MALEIMIDE COPOLYMER AND THERMOPLASTIC RESIN COMPOSITION COMPRISING THE COPOLYMER

Abstract: A process for producing a maleimide copolymer by emulsion polymerization of an aromatic vinyl monomer, a vinyl cyanide monomer, and a maleimide monomer in a specific mixture ratio, which comprises feeding an aromatic vinyl monomer in an amount more than a specified amount and, if necessary, a vinyl cyanide in an amount less than a specified amount before initiation of the polymerization, and adding continuously or by portions thereto, after initiation of the polymerization, the rest of the monomer mixture including the whole amount of a maleimide monomer, while keeping the pH of the aqueous phase of the polymerization system at 3 to 9 upon initiation of polymerization and using a redox catalyst comprising an oil-soluble organic peroxide. This process provides a maleimide copolymer having good heat resistance and heat decomposition resistance in a high yield. A thermoplastic resin composition prepared by com­ pounding the maleimide copolymer with a rubber reinforced resin obtained by grafting a vinyl cyanide monomer to a specified elastomer in a specified proportion, which may optionally be further blended with a thermoplastic resin hard at room temperature, is also disclosed. The resin composition has excellent heat resistance, heat decom­ position resistance, and impact resistance.

Description: Technical Field The invention relates to a process for the preparation of maleimide copolymers having excellent thermal resistance, and resistance to thermal decomposition, as well as to a thermoplastic resin composition comprising the maleimide copolymer and having excellent thermal resistance, resistance to thermal decomposition, and impact resistance. Prior Art In recent years, the demand for improved thermal resistance of materials for automobile parts has grown. In particular for the manufacture of interior trim parts such as meter hoods, meter clusters, instrument panels and console boxes, and of exterior trim parts such as bumpers, outer panels and lamp housings, a material having high thermal resistance, good moldability, and less subject to thermal decomposition and thermal discoloration is in demand. Conventionally, heat-resistant ABS resins, modified polyphenylene ether (modified PPE) resins, polycarbonate (PC) resins and similar resins have been used for the manufacture of automobile parts requiring thermal resistance. Heat-resistant ABS resins are prepared by the so-called graft blending of (i) a grafted ABS resin formed by grafting acrylonitrile and styrene and/or α-methylstyrene onto a diene rubber and (ii) a resin formed by the copolymerization of acrylonitrile with styrene and/or α-methylstyrene. In the existing circumstances, however, the resulting heat-resistant ABS resins fail to exhibit satisfactorily high thermal resistance because of the inadequate thermal resistance of the copolymer resin (ii) used. Although highly heat-resistant resins can be obtained by increasing the α-methylstyrene content of this copolymer resin (ii), copolymer resins (ii) having such a high α-methylstyrene content are disadvantageous in that resins having a high degree of polymerization cannot be obtained because of their low polymerization rate and in that they are subject to thermal decomposition during molding because of their structure including α-methylstyrene chains connected to each other. On the other hand, modified PPE resins and PC resins or their modified products generally have the disadvantage of being expensive and poor in moldability. Accordingly, there is a great need to develop a thermoplastic resin composition that is inexpensive, undergoes almost no thermal decomposition, can be molded easily, and has adequately high thermal resistance. It is already known that maleimide monomers of the formula where R is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, a cyclohexyl group, an aryl group or a substituted aryl group, can readily copolymerize with vinyl monomers, such as styrene, acrylonitrile or methyl methacrylate to form copolymers which have high thermal resistance but are very brittle. The polymerization techniques whereby highly heat-resistant resins can be prepared from maleimide monomers include solution polymerization, bulk polymerization, suspension polymerization and emulsion polymerization. However, from the viewpoint of uniformity characteristics such as the compositional distribution of each component in the copolymer and the distribution of polymerization degree, emulsion polymerization is considered to be suitable. Moreover, from the viewpoint of moldability, impact resistance and thermal resistance, it is expected that a desirable combination of properties are obtained in copolymers formed by copolymerizing a maleimide monomer with an aromatic vinyl monomer and a vinyl cyanide monomer. However, if an aromatic vinyl monomer, a vinyl cyanide monomer and a maleimide monomer are subjected to emulsion polymerization with a view to preparing a copolymer having high thermal resistance and resistance to thermal decomposition and thermal discoloration, a copolymer having low polymer yield and low thermal resistance and exhibiting poor impact resistance only will be obtained if the total amount of the monomer mixture is simply charged into the polymerization system at one time and the polymerization is then initiated. The reason for this may be that a charge-transfer complex is formed between the maleimide monomer and the aromatic vinyl monomer. Since this charge-transfer complex has high polymerizability, the complex is preferentially polymerized in the earlier stages of the polymerization, so that a copolymer having wide compositional distribution and molecular weight distribution is formed. Moreover, it has also been found that, when an aromatic vinyl monomer, a vinyl cyanide monomer and a maleimide monomer are polymerized by adding the total amount of a mixture of these monomers continuously to the polymerization system, the polymer yield is low and the resulting copolymer has poor resistance to thermal decomposition and low thermal resistance. JP-A-58-162616 discloses a process for the production of a maleimide copolymer with a maleimide monomer content of less than 50 mole %, which process is characterized in that the maleimide monomer is fed into a polymerization system containing a vinyl monomer consisting mainly of an aromatic vinyl monomer at a feed rate not higher than the consumption rate of the vinyl monomer resulting in copolymerization. The polymerization method is not limited, and it is described that such methods as solution polymerization, bulk polymerization, suspension polymerization and emulsion polymerization are applicable. According to the examples showing an emulsion polymerization, styrene is first added to the reaction vessel, then a mixture of N-lauryl maleimide, styrene and acrylonitrile is added dropwise for copolymerisation. This disclosure relates to a two-step polymerization process and does not describe nor suggest to use more and specific steps in the polymerization reaction. JP-A-59-135210 discloses a process for preparing maleimide copolymers by a two-step polymerization. In the second polymerization step of the cited process, a monomer mixture consisting of the remainder of the vinyl cyanide monomer and the maleimide or its derivative is polymerized. This document also does not describe nor suggest to use specific multi-steps in the polymerization reaction. Disclosure of the Invention It is an object of the present invention to provide a process for the preparation of maleimide copolymers having excellent thermal resistance, and undergoing almost no thermal decomposition or thermal discoloration during molding. It is another object of the present invention to provide an emulsion polymerization process for the preparation of maleimide copolymers which process can bring about high polymer yield and excellent polymerization stability and can yield copolymers having good resistance to thermal decomposition. It is still another object of the present invention to provide a thermoplastic resin composition containing a maleimide copolymer and having excellent thermal resistance, resistance to thermal decomposition, and impact resistance. According to the present invention, there is provided a process for the preparation of maleimide copolymers by emulsion polymerization of 50 to 80% by weight of an aromatic vinyl monomer, 10 to 30% by weight of a vinyl cyanide monomer, and 5 to 40% by weight of a maleimide monomer of the formula (A) where R is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, a cyclohexyl group, an aryl group or a substituted aryl group, provided that the total amount of said monomers is 100% by weight, said process comprising charging not less than 30% by weight of the total amount of said aromatic vinyl monomer into the polymerization system before initiation of said polymerization; adding a mixture composed of 70 to 95% by weight of the total amount of said vinyl cyanide monomer, the total amount of said maleimide monomer of the formula (A), and the remainder, if any, of said aromatic vinyl monomer into the polymerization system after initiation of the polymerization; and then adding the remaining 30 to 5% by weight of said vinyl cyanide monomer into the polymerization system; maintaining the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of said polymerization; and using a redox catalyst containing an oil-soluble organic peroxide. According to the present invention there is also provided a resin composition having excellent thermal resistance, said resin composition being formed by blending (I) a maleimide-copolymer prepared by emulsion polymerizing 50 to 80% by weight of an aromatic vinyl monomer, 10 to 30% by weight of a vinyl cyanide monomer, and 5 to 40% by weight of a maleimide monomer of the formula (A) where R is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, a cyclohexyl group, an aryl group or a substituted aryl group, provided that the total amount of said monomers is 100% by weight, said process being carried out by a) charging not less than 30% by weight of the total amount of said aromatic vinyl monomer into the polymerization system before initiation of said polymerization; b) adding a mixture composed of 70 to 95% by weight of the total amount of said vinyl cyanide monomer, the total amount of said maleimide monomer of the formula (A), and the remainder, if any, of said aromatic vinyl monomer to the polymerization system after initiation of said polymerization; and then c) adding the remaining 30 to 5% by weight of said vinyl cyanide monomer to the polymerization system; and maintaining the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of said polymerization; and using a redox catalyst containing an oil-soluble organic peroxide, with (II) a rubber-reinforced resin obtained by grafting one or more monomers selected from the group consisting of a vinyl cyanide monomer, an aromatic vinyl monomer and an acrylic monomer onto an elastomer having a glass transition temperature of 0°C or below, in a weight ratio of (I) to (II) ranging from about 5/95 to 95/5; and optionally blending 100 parts of the resulting thermoplastic resin composition with 0 to 300 parts by weight of a thermoplastic resin that is hard at room temperature. According to the present invention there is also provided a process for the preparation of maleimide copolymers by emulsion polymerization of 50 to 80% by weight of an aromatic vinyl monomer, 10 to 30% by weight of a vinyl cyanide monomer, and 5 to 40% by weight of a maleimide monomer of the formula (A) where R is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, a cyclohexyl group, an aryl group or a substituted aryl group, provided that the total amount of said monomers is 100% by weight, said process comprising charging not less than 30 % by weight of the total amount of said aromatic vinyl monomer and 5 to 40% by weight of the total amount of said vinyl cyanide monomer into the polymerization system before initiation of said polymerization; adding a mixture composed of 40 to 80% by weight of the total amount of said vinyl cyanide monomer, the total amount of said maleimide monomer of the formula (A), and the remainder, if any, of said aromatic vinyl monomer to the polymerization system after initiation of said polymerization; and then adding the remaining 5 to 25% by weight of said vinyl cyanide monomer to the polymerization system; maintaining the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of said polymerization; and using a redox catalyst containing an oil-soluble organic peroxide. According to the present invention there is also provided a resin composition having excellent thermal resistance, resistance to thermal decomposition, and impact resistance, said resin composition being formed by blending (I) a maleimide copolymer prepared by emulsion polymerizing 5o to 80% by weight of an aromatic vinyl monomer, 10 to 30% by weight of a vinyl cyanide monomer, and 5 to 40% by weight of a maleimide monomer of the formula (A) where R is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, a cyclohexyl group, an aryl group or a substituted aryl group, provided that the total amount of said monomers is 100% by weight, said process being carried out by a) charging not less than 30% by weight of the total amount of said aromatic vinyl monomer and 5 to 40% by weight of the total amount of said vinyl cyanide monomer into the polymerization system before initiation of said polymerization; b) adding a mixture composed of 40 to 80% by weight of the total amount of said vinyl cyanide monomer, the total amount of said maleimide monomer of the formula (A), and the remainder, if any, of said aromatic vinyl monomer to the polymerization system after initiation of said polymerization; and then c) adding the remaining 5 to 25% by weight of said vinyl cyanide monomer to the polymerization system; and maintaining the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of said polymerization; and using a redox catalyst containing an oil-soluble organic peroxide, with (II) a rubber-reinforced resin obtained by grafting one or more monomers selected from the group consisting of a vinyl cyanide monomer, an aromatic vinyl monomer and an acrylic monomer onto an elastomer having a glass transition temperature of 0°C or below, in a weight ratio of (I) to (II) ranging from about 5/95 to 95/5; and optionally blending 100 parts of the resulting thermoplastic resin composition with 0 to 300 parts by weight of a thermoplastic resin that is hard at room temperature. Best Mode for Carrying Out the Invention In the present process for the preparation of maleimide copolymers, the aromatic vinyl monomer should be used in an amount of 50 to 80% by weight. than 50% by weight, the resulting copolymer will have poor processability and fail to exhibit adequate impact strength, while if it is greater than 80% by weight, the proportion of the available maleimide monomer will be reduced and, therefore, a copolymer having low thermal resistance only will be obtained. The vinyl cyanide monomer should be used in an amount of 10 to 30% by weight. If the amount of vinyl cyanide monomer used is less than 10% by weight, the resulting copolymer will have poor processability and fail to exhibit adequate impact strength, while if it is greater than 30% by weight, a copolymer subject to thermal discoloration during processing only will be obtained. The maleimide monomer of the formula (A) should be used in an amount of 5 to 40% by weight. If the amount of maleimide monomer used is less than 5% by weight, the resulting copolymer will have low thermal resistance, while if it is greater than 40% by weight, a copolymer exhibiting poor impact strength only will be obtained. It is essential to charge not less than 30% by weight of the total amount of aromatic vinyl monomer used into the polymerization system before initiation of the polymerization. If the amount of aromatic vinyl monomer initially charged is less than 30% by weight, the polymer yield will be low and the resulting copolymer will have low thermal resistance. In the process of the present invention, the maleimide monomer of the formula (A) is not charged into the polymerization system before initiation of the polymerization. As stated above, the maleimide monomer forms a charge-transfer complex with the aromatic vinyl monomer. Accordingly, if the maleimide monomer is initially charged into the polymerization system, a copolymer having wide compositional distribution and molecular weight distribution will be formed. The vinyl cyanide monomer, the maleimide monomer and the remainder, if any, of the aromatic vinyl monomer may be added separately. However, it is desirable to add the vinyl cyanide monomer, the maleimide monomer and the remainder of the aromatic vinyl monomer in the form of a mixture. In the present invention, the polymerization is preferably carried out by charging not less than 30% by weight of the total amount of the aromatic vinyl monomer into the polymerisation system before initiation of the polymerization; adding a mixture composed of 70 to 95% by weight of the total amount of the vinyl cyanide monomer, the total amount of the maleimide monomer of the formula (A), and the remainder, if any, of the aromatic vinyl monomer into the polymerization system after initiation of the polymerization; and then adding, the remaining 30 to 5% by weight of the vinyl cyanide monomer into the polymerization system. Alternatively, the polymerization may be carried out by charging not less than 30% by weight of the total amount of the aromatic vinyl monomer and 5 to 40% by weight of the total amount of the vinyl cyanide monomer into the polymerization system before initiation of the polymerization; adding a mixture composed of 40 to 80% by weight of the total amount of the vinyl cyanide monomer, the total amount of the maleimide monomer of the formula (A), and the remainder, if any, of the aromatic vinyl monomer to the polymerization system after initiation of the polymerization; and then adding the remaining 5 to 25% by weight of the vinyl cyanide monomer to the polymerization system. Thus, when the polymerization is carried out by adding the vinyl cyanide monomer dividedly, the compositional distribution of the resulting copolymer is made uniform and, as a result, the resin compositions obtained by blending it with a rubber-reinforced resin will show a desired improvement in impact resistance. In the practice of the present invention, it is essential to maintain the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of the polymerization. In an aqueous solution exceeding pH 9, the maleimide monomer is liable to hydrolysis and, as a result, the polymer yield will be lowered and the stability of the polymerization system will be reduced. If the pH is lower than 3, the surface activity of the emulsifier will be reduced and, as a result, the polymer yield will undesirably be lowered. In the present process for the preparation of maleimide copolymers, the aromatic vinyl monomer may include one or more monomers selected from styrene, α-methylstyrene, tert-butylstyrene, chlorostyrene and vinyltoluene. The vinyl cyanide monomer may include one or more monomers selected from acrylonitrile, methacrylonitrile and fumaronitrile. The maleimide monomers represented by the above formula (A) include, for example, maleimide, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-isopropylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-o-chlorophenylmaleimide, N-toluylmaleimide, N-xylylmaleimide, N-naphthylmaleimide and N-tert-butylmaleimide. Among these maleimide monomers, N-phenylmaleimide, N-methylmaleimide, N-cyclohexylmaleimide and N-o-chlorophenylmaleimide are preferred, and N-phenylmaleimide is especially preferred. In the present process for the preparation of maleimide copolymers, other vinyl monomers which are copolymerizable with the aforesaid aromatic vinyl monomers, vinyl cyanide monomers and maleimide monomers may be used in an amount of up to 40% by weight of total amount of all monomers. Such other copolymerizable vinyl monomers comprise acrylic monomers including alkyl methacrylates such as methyl methacrylate and butyl methacrylate, and alkyl acrylates such as methyl acrylate and butyl acrylate. These other vinyl monomers can be added at any desired stage of the polymerization. The emulsifier used in the present invention comprises preferably an anionic emulsifier having emulsifying activity in the pH range of 3 to 9, and examples of such anionic emulsifiers include alkali metal salts of dodecylbenzenesulfonic acid, alkali metal salts of (alkyldiphenyl ether)disulfonic acids, alkali metal salts of alkylnaphthalenesulfonic acids, alkali metal salts of laurylsulfuric acid and sarcosinate. These emulsifiers may be used in combination. As the polymerization initiator, there is used a redox catalyst containing an oil-soluble organic peroxide. Especially preferred is a catalyst system composed of an oil-soluble organic peroxide, ferrous sulfate, a chelating agent and a reducing agent. If water-soluble initiators such as persulfates are used, the polymerization rate and the productivity will be low and the resulting copolymer will have poor resistance to thermal colorability and resistance to thermal decomposition. Preferred examples of oil-soluble organic peroxide polymerization initiators include cumene hydroperoxide, diisopropylbenzene hydroperoxide and tert-butyl hydroperoxide. As the reducing agent, there may be used formaldehyde sodium sulfoxylate, glucose and sodium ascorbate. In addition, it is especially desirable to use ferrous sulfate and a chelate compound such as sodium pyrophosphate or sodium ethylenediaminetetraacetate. If the maleimide copolymer thus obtained is used alone, it may be brittle and exhibit relatively low impact resistance. In order to improve its inadequate impact resistance, it is very effective to blend it with a rubber-reinforced resin formed by grafting a vinyl monomer onto an elastomer. In addition to the rubber-reinforced resin, a thermoplastic resin which is hard at room temperature, such as a polycarbonate (PC) resin or a polybutylene terephthalate (PBT) resin, may optionally be used in combination for the purpose of further improving the impact resistance. Moreover, in order to improve the processability of the maleimide copolymer, it is also effective to use an acrylonitrile-styrene copolymer resin (AS resin) or an acrylonitrile-α-methylstyrene copolymer resin (αSAN resin) in combination therewith. The elastomer present in the rubber-reinforced resin to be blended with the maleimide copolymer should have a glass transition temperature of 0°C or below. Specific examples of such elastomers are as follows: Diene elastomers such as a polybutadiene or a copolymer composed mainly of butadiene and formed by copolymerizing it with at least one monomer selected from acrylonitrile, styrene, methyl methacrylate, and acrylic esters having an alkyl group of 1 to 8 carbon atoms; acrylic elastomers such as a polymer of an acrylic ester having an alkyl group of 1 to 8 carbon atoms or a copolymer composed mainly of such an acrylic ester and formed by copolymerizing it with at least one monomer selected from acrylonitrile, styrene and methyl methacrylate; ethylene-propylene copolymer rubber; ethylene-propylene-nonconjugated diene copolymer rubbers (EPDM rubbers); silicone rubber; and chlorinated polyethylene. Among diene elastomers, polybutadiene, styrene-butadiene copolymer rubber and acrylonitrile-butadiene copolymer rubber are preferred. Moreover, polybutyl acrylate, acrylonitrile-butyl acrylate copolymers and EPDM rubbers may also be preferably used as the elastomer. The monomer to be grafted onto the above-defined elastomer preferably comprises at least one monomer selected from vinyl cyanide monomers such as acrylonitrile, methacrylonitrile and fumaronitrile; aromatic vinyl monomers such as styrene, α-methylstyrene, tert-butylstyrene, vinyltoluene, chlorostyrene and bromostyrene, especially, styrene, α-methylstyrene, tert-butylstyrene and vinyltoluene; and acrylic monomers including alkyl methacrylates (such as methyl methacrylate), alkyl acrylates (such as methyl acrylate, ethyl acrylate and butyl acrylate). Commercially available examples of rubber-reinforced resins formed by grafting a monomer selected from the above-described group of monomers onto an elastomer as defined above include ABS resins (acrylonitrile-butadiene-styrene copolymer resins), MBS resins (methyl methacrylate-butadiene-styrene copolymer resins), AAS resins (acrylonitrile-acrylic rubber-styrene copolymer resins), AES resins (acrylonitrile-EPDM rubber-styrene copolymer resins) and ACS resins (acrylonitrile-chlorinated polyethylene-styrene copolymer resins). The techniques whereby the monomer can be grafted onto the above-defined elastomer include emulsion polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion/suspension polymerization and emulsion/bulk polymerization. The thermoplastic resins that are hard at room temperature include AS resins, methyl methacrylate resin, methyl methacrylate-styrene copolymer resins, αSAN resins, PC resins, unmodified or modified PPE resins, maleic anhydride-styrene copolymer resins, maleic anhydride-acrylonitrile-styrene copolymer resins, polyester resins such as PBT resin and polyethylene terephthalate, (PET) resin, polyamide resins such as 6-nylon and 66-nylon. Among these resins, acrylonitrile-styrene resins, acrylonitrile-α-methylstyrene copolymer resins, polycarbonate resins, methyl methacrylate resins, methyl methacrylate-styrene copolymer resins, polyester resins, polyamide resins and polyphenylene ether resins are preferred. These resins may be used in combination. In order to improve processability, it is effective to use an AS resin or αSAN resin. Moreover, PC resins are effective for the improvement of impact strength. PBT resin, PET resin and polyamide resins are effective for the improvement of chemical resistance and practical thermal resistance. The proportion (or weight ratio) of the maleimide copolymer (I) to the rubber-reinforced resin (II) may suitably range from 5/95 to 95/5. If the amount of the rubber-reinforced resin is less than 5% by weight, the resulting composition may have unacceptably low impact resistance. On the other hand, if it is more than 95% by weight, the resulting composition will not show an improvement in thermal resistance. Where a hard thermoplastic resin is added to the aforesaid blend of the maleimide copolymer (I) and the rubber-reinforced resin (II), the hard thermoplastic resin is suitably used in an amount of 0 to 300 parts by weight per 100 parts by weight of the blend of the maleimide copolymer (I) and the rubber-reinforced resin (II). If the amount of hard thermoplastic resin used is more than 300 parts by weight, the proportions of the maleimide copolymer and the rubber-reinforced resin will become so low that no improvement in thermal resistance and impact resistance can be expected. Moreover, hindered phenol antioxidants and phosphite stabilizers may be added to the aforesaid composition for the purpose of improving its thermal stability; benzophenone UV absorbers, hindered amine stabilizers and benzotriazole UV absorbers may be added thereto for the purpose of improving its weather resistance; and amide type lubricants (such as ethylene-bis-stearamide and metallic soaps may be added thereto for the purpose of improving its processability. These additives may be used alone or in combination. By adding a flame retarder or similar additive, the thermoplastic resin composition of the present invention may also be utilized as a flame-retardant resin. The thermoplastic resin compositions prepared in accordance with the present invention can be utilized in various fields of processing applications such as injection molding, extrusion molding and vacuum forming. Moreover, the articles so formed can be subjected to sheen treatments such as plating, vacuum deposition and sputtering. Furthermore, they can also be coated or painted. The present invention is more specifically explained with reference to the following examples. In these examples, parts are by weight. Example 1 Preparation of maleimide copolymer I-1 : A 20-liter glass reactor (equipped with a stirrer, a condenser and a thermometer) was thoroughly purged with nitrogen and charged with the following materials (initial charge composition): Purified water 200 parts Sodium dodecylbenzenesulfonate 2 parts Sodium sulfate 0.2 parts Disodium ethylenediaminetetraacetate (EDTA-2Na) 0.01 parts Ferrous sulfate heptahydrate (FeSO₄·7H₂O) 0.002 parts Rongalite 0.5 parts When the composition in the reactor was intimately mixed by stirring, its pH was found to be 8.6. Then, 70 parts of α-methylstyrene were added thereto and intimately mixed therewith, and the resulting mixture was heated to 70°C. Thereafter, the polymerization was initiated by dropwise adding the following additive monomers (1) to the reaction system at 70°C over a period of 150 minutes: Additive monomers (1) Acrylonitrile 10 parts N-phenylmalimide 15 parts Cumene hydroperoxide (CHP) 0.5 parts tert-Dodecyl mercaptan 0.1 parts Following the addition of the additive monomers (1), 5 parts of acrylonitrile were continuously added dropwise as the additive monomer (2). After completion of the addition, the reaction system was heated to 80°C, 0.1 parts of CHP were added thereto, and the polymerization was continued at 80°C for additional 2 hours. After completion of the polymerization, the pH of the reaction system was 4.0. The polymer yield of the resulting latex was 94%. This latex was coagulated with 3% magnesium sulfate at a temperature of 90°C or above, and the resulting coagula were dehydrated, washed with water, and then dried to obtain a white powder. The white powder thus obtained was mixed with 0.2 parts of a phenolic antioxidant (Antage W-400; trade name) and 0.4 parts of a phosphite stabilizer (Mark C; trade name) in a Henschel mixer, and then pelletized by extrusion at 260°C with a twin-screw extruder (PCM-30; trade name). Using a 1-ounce injection molding machine (SAV-30A; trade name), the pellets thus obtained were molded into flat plates having a size of 50 x 80 x 3 mm. Flat plates molded at 250°C were used to determine the Vicat softening temperature and the glass transition temperature of the copolymer. Separately, a flat plate molded at 290°C was used to evaluate the thermal decomposability of the copolymer on the basis of the presence or absence of silver streaks on the surface thereof. The composition of the polymerization system and the results of polymerization are shown in Table 1, and the results of evaluation of various properties of the molded plates are shown in Table 2. Examples 2-7 and Comparative Examples 1-2 Polymerization, coagulation, extrusion and evaluation were carried out in the same manner as described in Example 1, except that the initial charge composition, the formulation of the additive monomers (1), and the amount of acrylonitrile used as the additive monomer (2) were modified as shown in Table 1. The results thus obtained are shown in Tables 1 and 2. The maleimide copolymers obtained in Examples 2 and 6 will hereinafter be referred to as maleimide copolymer I-2 and I-3, respectively. Comparative Example 3 (simultaneous addition of all monomers) Preparation of maleimide copolymer I-4 : A reactor similar to that used in Example 1 was purged with nitrogen and then charged with the following materials (initial charge composition): Purified water 200 parts Sodium dodecylbenzenesulfonate 2 parts sodium sulfate 0.2 parts EDTA-2Na 0.01 parts FeSO₄·7H₂O 0.002 parts Rongalite 0.5 parts The composition in the reactor was intimately mixed by stirring and then heated to 70°C. Thereafter, the following materials were added dropwise thereto over a period of 150 minutes: Acrylonitrile 15 parts α-methylstyrene 70 parts N-phenylmaleimide 15 parts CHP 0.5 parts tert-Dodecyl mercaptan 0.1 parts After completion of the addition, the reaction system was heated to 80°C, 0.1 parts of CHP were added thereto, and the polymerization was continued for an additional 2 hours. The polymer yield had a relatively low value of 90%. The resulting latex was coagulated, extruded and evaluated in the same manner as described in Example 1. The results thus obtained are shown in Table 2. Comparative Example 4 (use of potassium persulfate as initiator) Preparation of maleimide copolymer I-5 : Polymerization was carried out in the same manner as described in Example 1, except that 0.5 parts of potassium persulfate were used in place of EDTA-2Na, FeSO₄·7H₂O and Rongalite, and CHP was excluded from the formulation of the additive monomer (1). The polymer yield of the resulting latex had a relatively low value of 85%. Comparative Example 5 (polymerization at pH 11) Polymerization was carried out in the same manner as described in Example 1, except that 0.2 parts of 10% sodium hydroxide were added to the initial charge composition so as to bring the pH of the polymerization system to 11. The polymer yield of the resulting latex had a relatively low value of 84%. Comparative Example 6 (polymerization at pH 2) Polymerization was carried out in the same manner as described in Example 1, except that 0.2 parts of 10% hydrochloric acid were added to the initial charge composition so as to bring the pH of the polymerization system to 2.0. The polymer yield of the resulting latex had a relatively low value of 81%. Example 8 Polymerization was carried out in the same manner as described in Example 1, except that the CHP included in the formulation of the additive monomer (1) was replaced by tert-butyl hydroperoxide. Thereafter, coagulation, extrusion and evaluation were carried out in the same manner as described in Example 1. The results thus obtained are shown in Tables 1 and 2. Example 9 Preparation of maleimide copolymer I-6 : A maleimide copolymer was prepared in the same manner as described in Example 1, except that the acrylonitrile constituting the additive monomer (2) was used in admixture with the additive monomers (1). Example 10 Preparation of maleimide copolymer I-7 : A 20-liter glass reactor (equipped with a stirrer, a condenser and a thermometer) was thoroughly purged with nitrogen and charged with the following materials (the initial charge composition): Purified water 200 parts Sodium dodecylbenzenesulfonate 2 parts Sodium sulfate 0.2 parts EDTA-2Na 0.01 parts FeSO₄·7H₂O 0.002 parts Rongalite 0.5 parts When the composition in the reactor was intimately mixed by stirring, its pH was found to be 8.6. Then, 30 parts of α-methylstyrene and 5 parts of acrylonitrile were added thereto and the resulting mixture was emulsified by stirring for 30 minutes. The resulting emulsion was heated to 60°C, and the polymerization was initiated by adding 0.05 parts of CHP. At the same time, the following materials were continuously added dropwise to the reaction system over a period of 150 minutes: Acrylonitrile 14 parts α-Methylstyrene 35 parts N-phenylmaleimide 13 parts CHP 0.5 parts Subsequently, 3 parts of acrylonitrile was added dropwise over a period of 10 minutes. Thereafter, the reaction system was maintained at 60°C for 2 hours to complete the polymerization. After completion of the polymerization, the pH of the reaction system was 4.2. The polymer yield of the resulting latex was 98%. This latex was coagulated with a 10% solution of magnesium sulfate at a temperature of 98°C, and the resulting coagula were dehydrated, washed with water, and then dried to obtain a white powder. The maleimide copolymers (Examples 1-10) prepared in accordance with the present invention had a high polymer yield and a small amount of coagula produced during the polymerization, thus showing good results. In contrast, when the polymerization was carried out by adding all monomers continuously (Comparative Example 3), the polymer yield was relatively low and large amounts of coagula were produced during the polymerization, so that this process was found to be unsuitable for purposes of industrial production. Similarly, when potassium persulfate was used as polymerization initiator (Comparative Example 4), the polymer yield was low and relatively large amounts of coagula were produced. Moreover, it is evident from Table 2 that the maleimide copolymers prepared in accordance with the present invention had high thermal resistance and were not subject to thermal decomposition. Synthesis Example 1 Preparation of graft polymer II-1 : A reactor was charged with the following materials: Polybutadiene latex (having an average particle diameter of 0.3 µm, a gel content of 80% and a degree of gel swelling of 25) 60 parts (on a solid basis) Purified water 140 parts Dextrose 0.6 parts Sodium pyrophosphate 0.3 parts FeSO₄·7H₂O 0.002 parts Potassium rosinate 1.0 part After the composition in the reactor was heated to 60°C, a mixture composed of 12 parts of acrylonitrile, 28 parts of styrene, 0.2 parts of CHP and 0.5 parts of tert-dodecyl mercaptan was continuously added dropwise to the reaction system over a period of 120 minutes. After completion of the addition, the reaction system was aged at 60°C for an additional 120 minutes to complete the polymerization. To the resulting latex were added 0.5 parts of 2,6-di-tert-butyl-p-cresol (BHT). After intimate mixing, the latex was coagulated with diluted sulfuric acid, dehydrated and then dried to obtain a white powder. Synthesis Example 2 Preparation of graft polymer II-2 : A reactor was charged with the following materials: Polybutadiene latex (having an average particle diameter of 0.3 µm, a gel content of 80% and a degree of gel swelling of 25) 45 parts (on a solid basis) Purified water 140 parts Dextrose 0.6 parts Sodium pyrophosphate 0.3 parts FeSO₄·7H₂O 0.002 parts Potassium rosinate 1 part Acrylonitrile 8.4 parts Styrene 19.6 parts After the composition in the reactor was heated to 60°C, the polymerization was initiated by adding 0.3 parts of CHP. After the polymerization was continued for 70 minutes, the second-stage polymerization was carried out by adding a mixture composed of 8.1 parts of acrylonitrile, 18.9 parts of α-methylstyrene and 0.2 part of CHP over a period of 1 hour. To the resulting graft polymer latex was added 0.4 part of BHT. Thereafter, the latex was coagulated with diluted sulfuric acid, dehydrated and then dried to obtain a white powder. Synthesis Example 3 Preparation of graft polymer II-3 : A reactor was charged with the following materials. Polybutadiene latex (having an average particle diameter of 0.3 µm, a gel content of 80% and a degree of gel swelling of 25) 60 parts (on a solid basis) Purified water 140 parts Potassium oleate 2 parts FeSO₄·7H₂O 0.003 parts Sodium pyrophosphate 0.3 parts Dextrose 1 part The composition in the reactor was heated to 60°C with stirring. While it was kept at 60°C, the polymerization was carried out by adding a mixture composed of 16 parts of styrene, 24 parts of methyl methacrylate, 0.2 parts of CHP and 0.3 parts of tert-dodecyl mercaptan continuously thereto, with stirring, over a period of 3 hours. Then, the reaction system was heated to 70°C and the polymerization was continued for an additional one hour to obtain a graft polymer latex. To the resulting graft polymer latex was added 0.5 parts of BHT. Thereafter, the latex was coagulated with sulfuric acid, dehydrated and then dried to obtain a white powder. As other rubber-reinforced resins to be blended with a maleimide copolymer, the following resins were used in pellet form: AAS resin (II-4): Dialac A#700 (trade name). AAS resin (II-5): Vitax V6101 (trade name). AES resin (II-6): JSR AES #100 (trade name). Examples 11-27 and Comparative Examples 7-15 Maleimide copolymers I-1 to I-7, rubber-reinforced resins (graft polymers) II-1 to II-6, and the hard thermoplastic resins given below were mixed in each of the proportions shown in Tables 3 and 4. Moreover, 0.2 part of a phenolic antioxidant (Antage W-400; trade name) and 0.4 parts of a phosphite stabilizer (Mark C; trade name) were added as stabilizers. After intimate mixing, each of the resulting blends was extruded at 260°C with a 30 mm twin-screw extruder to obtain a thermoplastic resin composition in pellet form. AS resin (acrylonitrile-styrene copolymer resin): According to the suspension polymerization technique, 30 parts of acrylonitrile and 70 parts of styrene were polymerized in the usual manner to form an AS resin. The resulting resin had an acrylonitrile content of 27% by weight and a specific viscosity (η sp /C) of 0.6. αSAN resin (acrylonitrile-α-methylstyrene copolymer resin): According to the emulsion polymerization technique, an αSAN resin having an acrylonitrile content of 20% by weight and a specific viscosity (η sp /C) of 0.5 was prepared in the usual manner. PC resin: Novalex 7022PJ (trade name) was used in pellet form. Using each of the thermoplastic resin compositions thus obtained in pellet form, flat plates having a size of 50 x 80 x 3 mm were injection molded at 290°C in the same manner as described in Example 1, and the thermal decomposability of the resin composition was evaluated by examining the number of silver streaks developed on the surface of a molded plate. Other properties were evaluated according to the following procedures: Izod impact strength: ASTM D-256 (in kg·cm/cm), notched 1/4" bar. Melt flow index: ASTM D-1238 (in g/10 min.), 230°C x 5 kg load. Rockwell hardness: ASTM D-785 (in R scale). Vicat softening : temperature ISO R-306 (in °C), 5 kg load. As shown in Examples 11-13 and 27, the blends of graft polymer II-1 (grafted ABS resin) and maleimide copolymers were markedly improved in thermal resistance (Vicat softening temperature) compared with the blend with AS resin (Comparative Example 11) and the blend with αSAN resin (Comparative Example 12). In Examples 14 and 15, graft polymer II-2 containing α-methylstyrene as a graft monomer was used. The use of this graft polymer was found to bring about a substantial improvement in impact strength compared with the use of graft polymer II-1 (Examples 11-13). Moreover, these blends were much superior in impact strength to the blend with αSAN resin (Comparative Example 15). In Example 16, graft polymer II-3 (grafted MBS resin) was used and the results of evaluation were substantially the same as those obtained with the grafted ABS resin. This indicates that grafted MBS resins are also effective in improving the impact strength of maleimide copolymers. Moreover, as is evident from Examples 17-19, the use of weather-resistant resins (such as AAS resins and AES resins) as rubber-reinforced resins is effective in the improvement of thermal resistance. Furthermore, as is evident from Examples 20 and 21, the incorporation of an AS resin into blends of a grafted ABS resin and a maleimide copolymer is effective in the improvement of melt flow index which is a measure of processability. It can be seen from Examples 22 and 23 that, when an αSAN resin is incorporated into blends of a grafted ABS resin and a maleimide copolymer, the resulting resin composition shows a slight improvement in processability while suffering little loss in thermal resistance. In addition, it is evident from Examples 24-26 that a resin composition having very high impact strength and excellent thermal resistance can be obtained by incorporating a PC resin thereinto.

Claims: A process for the preparation of maleimide copolymers by emulsion polymerization of 50 to 80% by weight of an aromatic vinyl monomer, 10 to 30% by weight of a vinyl cyanide monomer, and 5 to 40% by weight of a maleimide monomer of the formula (A) where R is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, a cyclohexyl group, an aryl group or a substituted aryl group, provided that the total amount of said monomers is 100% by weight, said process comprising charging not less than 30% by weight of the total amount of said aromatic vinyl monomer into the polymerization system before initiation of said polymerization; adding a mixture composed of 70 to 95% by weight of the total amount of said vinyl cyanide monomer, the total amount of said maleimide monomer of the formula (A), and the remainder, if any, of said aromatic vinyl monomer into the polymerization system after initiation of the polymerization; and then adding the remaining 30 to 5% by weight of said vinyl cyanide monomer into the polymerization system; maintaining the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of said polymerization; and using a redox catalyst containing an oil-soluble organic peroxide. A process as claimed in Claim 1 wherein said aromatic vinyl monomer comprises at least one monomer selected from the group consisting of styrene, α-methylstyrene, tertbutylstyrene, chlorostyrene and vinyltoluene. A process as claimed in claim 1 or 2 wherein said vinyl cyanide monomer comprises at least one monomer selected from the group consisting of acrylonitrile, methacrylonitrile and fumaronitrile. A process as claimed in any one of the Claims 1 to 3 wherein said maleimide monomer of the formula (A) comprises at least one monomer selected from the group consisting of N-phenylmaleimide, N-methylmaleimide, N-cyclohexylmaleimide and N-o-chlorophenylmaleimide. A process for the preparation of maleimide copolymers by emulsion polymerization of 50 to 80% by weight of an aromatic vinyl monomer, 10 to 30% by weight of a vinyl cyanide monomer, and 5 to 40% by weight of a maleimide monomer of the formula (A) where R is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, a cyclohexyl group, an aryl group or a substituted aryl group, provided that the total amount of said monomers is 100% by weight, said process comprising charging not less than 30 % by weight of the total amount of said aromatic vinyl monomer and 5 to 40% by weight of the total amount of said vinyl cyanide monomer into the polymerization system before initiation of said polymerization; adding a mixture composed of 40 to 80% by weight of the total amount of said vinyl cyanide monomer, the total amount of said maleimide monomer of the formula (A), and the remainder, if any, of said aromatic vinyl monomer to the polymerization system after initiation of said polymerization; and then adding the remaining 5 to 25% by weight of said vinyl cyanide monomer to the polymerization system; maintaining the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of said polymerization; and using a redox catalyst containing an oil-soluble organic peroxide. A process as claimed in Claim 5 wherein said aromatic vinyl monomer comprises at least one monomer selected from the group consisting of styrene, α-methylstyrene, tert-butylstyrene, chlorostyrene and vinyltoluene. A process as claimed in Claim 5 or 6 wherein said vinyl cyanide monomer comprises at least one monomer selected from the group consisting of acrylonitrile, methacrylonitrile and fumaronitrile. A process as claimed in any one of Claim 5 to 7 wherein said maleimide monomer of the formula (A) comprises at least one monomer selected from the group consisting of N-phenylmaleimide, N-methylmaleimide, N-cyclohexylmaleimide and N-o-chlorophenylmaleimide. A resin composition having excellent thermal resistance, resistance to thermal decomposition, and impact resistance, said resin composition being formed by blending (I) a maleimide copolymer prepared by emulsion polymerizing 50 to 80% by weight of an aromatic vinyl monomer 10 to 30% by weight of a vinyl cyanide monomer, and 5 to 40% by weight of a maleimide monomer of the formula (A) where R is a hydrogen atom, an alkyl group of 1 to 4 atoms, a cyclohexyl group, an aryl group or a substituted aryl group, provided that the total amount of said monomers is 100% by weight, said process being carried out by a) charging not less than 30% by weight of the total amount of said aromatic vinyl monomer into the polymerization system before initiation of said polymerization; b) adding a mixture composed of 70 to 95% by weight of the total of said vinyl cyanide monomer, the total amount of said maleimide monomer of the formula (A), and the remainder, if any, of said aromatic vinyl monomer to the polymerization system after initiation of said polymerization; and then c) adding the remaining 30 to 5% by weight of said vinyl cyanide monomer to the polymerization system; and maintaining the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of said polymerization; and using a redox catalyst containing an oil-soluble organic peroxide, with (II) a rubber-reinforced resin obtained by grafting one or more monomers selected from the group consisting of a vinyl cyanide monomer, an aromatic vinyl monomer and an acrylic monomer onto an elastomer having a glass transition temperature of 0°C or below, in a weight ratio of (I) to (II) ranging from about 5/95 to 95/5; and optionally blending 100 parts of the resulting thermoplastic resin composition with 0 to 300 parts by weight of a thermoplastic resin that is hard at room temperature. The resin composition as claimed in Claim 9, wherein in said maleimide copolymer (I), said aromatic vinyl monomer comprises at least one monomer selected from the group consisting of styrene, α-methylstyrene, tert-butylstyrene, chlorostyrene and vinyltoluene. The resin composition as claimed in Claim 9 or 10 wherein in said maleimide copolymer (I), said vinyl cyanide monomer comprises at least one monomer selected from the group consisting of acrylonitrile, methacrylonitrile and fumaronitrile. The resin composition as claimed in anyone of Claims 9 to 11, wherein said maleimide monomer of the formula (A) comprises at least one monomer selected from the group consisting of N-phenylmaleimide, N-methylmaleimide, N-cyclohexylmaleimide and N-o-chlorophenylmaleimide. The resin composition as claimed in any one of Claims 9 to 12, wherein said elastomer having a glass transition temperature of 0°C or below comprises at least one elastomer selected from the group consisting of polybutadiene, styrene-butadiene rubber and acrylonitrile-butadiene rubber. The resin composition as claimed in any one of Claims 9 to 12, wherein said elastomer having a glass transition temperature of 0°C or below comprises at least one elastomer selected from the group consisting of polybutyl acrylate, acrylonitrile-butyl acrylate copolymers, styrene-butyl acrylate copolymers and ethylene-propylene-nonconjugated diene copolymer rubbers. The resin composition as claimed in any one of Claims 9 to 14, wherein said vinyl cyanide monomer to be grafted onto said elastomer comprises at least one monomer selected from the group consisting of acrylonitrile, methacrylonitrile and fumaronitrile. The resin composition as claimed in any one of Claims 9 to 15, wherein said aromatic vinyl monomer to be grafted onto said elastomer comprises at least one monomer selected from the group consisting of styrene, α-methylstyrene, tert-butylstyrene and vinyltoluene. The resin composition as claimed in anyone of Claims 9 to 16 wherein said acrylic monomer to be grafted onto said elastomer comprises at least one monomer selected from the group consisting of methyl methacrylate, methyl acrylate, ethyl acrylate and butyl acrylate. The resin composition as claimed in Claim 9, wherein said thermoplastic resin that is hard at room temperature comprises at least one resin selected from the group consisting of acrylonitrile-styrene copolymer resins, acrylonitrile-α-methylstyrene copolymer resins, methyl methacrylate resins, methyl methacrylate-styrene copolymer resins, polycarbonate resins, polyester resins, polyamide resins and polyphenylene ether resins. A resin composition having excellent thermal resistance, resistance to thermal decomposition, and impact resistance, said resin composition being formed by blending (I) a maleimide copolymer prepared by emulsion polymerizing 50 to 80% by weight of an aromatic vinyl monomer, 10 to 30% by weight of a vinyl cyanide monomer, and 5 to 40% by weight of a maleimide monomer of the formula (A) where R is a hydrogen atom, an alkyl group of 1 to 4 carbon atoms, a cyclohexyl group, an aryl group or a substituted aryl group, provided that the total amount of said monomers is 100% by weight, said process being carried out by a) charging not less than 30% by weight of the total amount of said aromatic vinyl monomer and 5 to 40% by weight of the total amount of said vinyl cyanide monomer into the polymerization system before initiation of said polymerization; b) adding a mixture composed of 40 to 80% by weight of the total of said vinyl cyanide monomer, the total amount of said maleimide monomer of the formula (A), and the remainder, if any, of said aromatic vinyl monomer to the polymerization system after initiation of said polymerization; and then c) adding the remaining 5 to 25% by weight of said vinyl cyanide monomer to the polymerization system; and maintaining the pH of the aqueous phase of the polymerization system in the range of 3 to 9 at the initiation of said polymerization; and using a redox catalyst containing an oil-soluble organic peroxide, with (II) a rubber-reinforced resin obtained by grafting one or more monomers selected from the group consisting of a vinyl cyanide monomer, an aromatic vinyl monomer and an acrylic monomer onto an elastomer having a glass transition temperature of 0°C or below, in a weight ratio of (I) to (II) ranging from about 5/95 to 95/5; and optionally blending 100 parts of the resulting thermoplastic resin composition with 0 to 300 parts by weigt of a thermoplastic resin that is hard at room temperature. The resin composition as claimed in Claim 19, wherein in said maleimide copolymer (I), said aromatic vinyl monomer comprises at least one monomer selected from the group consisting of styrene, α-methylstyrene, tert-butylstyrene, chlorostyrene and vinyltoluene. The resin composition as claimed in Claim 19 or 20 wherein in said maleimide copolymer (I), said vinyl cyanide monomer comprises at least one monomer selected from the group consisting of acrylonitrile, methacrylonitrile and fumaronitrile. The resin composition as claimed in any one of the Claims 19 to 21, wherein said maleimide monomer of the formula (A) comprises at least one monomer selected from the group consisting of N-phenylmaleimide, N-methylmaleimide, N-cyclohexylmaleimide and N-o-chlorophenylmaleimide. The resin composition as claimed in any one of the Claims 19 to 22, wherein said elastomer having a glass transition temperature of 0°C or below comprises at least one elastomer selected from the group consisting of polybutadiene, styrene-butadiene rubber and acrylonitrile-butadiene rubber. The resin composition as claimed in any one of the Claims 19 to 22, wherein said elastomer having a glass transition temperature of 0°C or below comprises at least one elastomer selected from the group consisting of polybutyl acrylate, acrylonitrile-butyl acrylate copolymers, styrene-butyl acrylate copolymers and ethylene-propylene-nonconjugated copolymer rubbers. The resin composition as claimed in any one of the Claims 19 to 24, wherein said vinyl cyanide monomer to be grafted onto said elastomer comprises at least one monomer selected from the group consisting of acrylonitrile, methacrylonitrile and fumaronitrile. The resin composition as claimed in any one of the Claims 19 to 25, wherein said aromatic vinyl monomer to be grafted onto said elastomer comprises at least one monomer selected from the group consisting of styrene, α-methylstyrene, tert-butylstyrene and vinyltoluene. The resin composition as claimed in any one of the Claims 19 to 26 wherein said acrylic monomer to be grafted onto said elastomer comprises at least one monomer selected from the group consisting of methyl methacrylate, methyl acrylate, ethyl acrylate and butyl acrylate. The resin composition as claimed in Claim 19, wherein said thermoplastic resin that is hard at room temperature comprises at least one resin selected from the group consisting of acrylonitrile-styrene copolymer resins, acrylonitrile-α-methylstyrene copolymer resins, methyl methacrylate resins, methyl methacrylate-styrene copolymer resins, polycarbonate resins, polyester resins, polyamide resins and polyphenylene ether resins.

Inventors: KIMURA, ATSUSHI, KISHIDA, KAZUO, TOYOOKA, YUTAKA
Applicants: MITSUBISHI RAYON CO., LTD.
Application year: 1986
Main classification: C08F212
IPC codes: C08F222