Heat resistant polyvinyl chloride copolymer and preparation process of the copolymer

Abstract: A heat resistant polyvinyl chloride copolymer or a heat and impact resistant polyvinyl chloride copolymer is prepared by conducting graft copolymerization of N-substituted maleimide on a vinyl chloride resin or a rubber containing vinyl chloride resin. The graft copolmerization reaction is carried out in the presence of a radical polymerizable monomer which is (1) liquid at the polymerization temperature, (2) capable of dissolving the N-substituted maleimide at the temperature, (3) 70°C or more in glass transition temperature of the polymer thereof, and (4) used in an amount sufficient to dissolve the N-substituted maleimide.

Description: The present invention relates to heat and impact resistant polyvinyl chloride copolymers and a process for the preparation of these copolymers. More particularly, it relates to a polyvinyl chloride copolymer which is excellent in heat resistance, thermal stability and processability and can be used for films, sheets, corrugated sheetings, pipes, cable ducts, deck plates, building materials and industrial components. It further relates to a heat resistant copolymer which has excellent impact resistance in addition to its heat resisting properties. Vinyl chloride resin has been widely used because rigid, semi-rigid and flexible products can be prepared by kneading the resin with a heat stabilizer, light stabilizer, plasticizer, lubricant, filler and coloring material. Particularly for rigid products, heat resistance of the molded articles has recently been required and hence vinyl chloride resin with improved heat resistance has been desired. So-called post-chlorinated vinyl chloride resin obtained by further chlorinating common vinyl chloride resin has been known to date as a vinyl chloride resin having improved heat resistance. Post-chlorinated vinyl chloride resin, however, has poor heat stability, is liable to discoloration and has disadvantages in terms of processability. Consequently, research for improvement of these resins has been continuing. For example, BP 1,293,542 discloses a thermoplastic resin composition obtained by blending a vinyl chloride base polymer with a copolymer composed of N-substituted maleimide and methacrylate ester monomer containing 50 % by weight or more of methyl methacrylate, or with a copolymer composed of N-substituted maleimide and said monomer in combination with other copolymerizable monomers. The composition, however, is still unsatisfactory in heat resistance. A resin obtained by copolymerizing vinyl chloride with N-cyclohexylmaleimide is known to have improved heat resistance. A method having specific preparation conditions for improving the heat resistance of this resin has been disclosed in Japanese Laid-Open Patent Publication No. 236809 /1987. In this disclosure, N-cyclohexylmaleimide is added portion by portion in a copolymerization with vinyl chloride. However, the polyvinyl chloride copolymer obtained by this process has insufficient thermal stability and impact resistance although its heat resistance is improved. As set forth above, vinyl chloride resin can provide products ranging from flexible to rigid as desired, is resistant to various chemicals and has good processability. However, further improvement in heat resistance, thermal stability and also impact resistance is required for the resin. An object of this invention is to provide polyvinyl chloride copolymers having excellent heat resistance and excellent impact resistance and a process for the preparation of such copolymers. GB-A-1015334 relates to the production of blends of vinyl chloride polymer and other thermoplastic polymers, particularly acrylic polymers. The problem presented is that of obtaining a homogeneous mixture and the teaching promises a simpler and more commercially attractive way of achieving this. The process taught involves forming an aqueous slurry of a polymer or copolymer of vinyl chloride and adding to it a further monoethylenically unsaturated monomer component, the important point being that the added monomer component is to be entirely absorbed into the polymer or copolymer by reason of the fact that the polymer or copolymer is porous or swells to form a gel-like structure. The further monomer component is then polymerised in situ in the presence of a free radical-yielding polymerization catalyst or initiator. Both alkyl acrylates and N-substituted maleimides are suggested for the monomer component to be absorbed and, as the last of 18 examples, one example is given in which methyl methacrylate and N-ortho-chlorophenyl maleimide are used together. No suggestion is made that one of these is a solvent for the other and the problem of producing moulded articles with improved heat resistance is not tackled. According to the present invention, a process is provided for the preparation of a heat resistant polyvinyl chloride copolymer by graft copolymerization of an N-substituted maleimide on a vinyl chloride resin, which comprises conducting the graft copolymerisation in the presence of a solvent polymerizable monomer which: (1) is a liquid at the polymerization temperature, (2) is capable of dissolving the N-substituted maleimide at that temperature, (3) has a glass transition temperature in the polymer state of at least 70°C, and (4) is used in an amount sufficient to dissolve the N-substituted maleimide, the amount of N-substituted maleimide being from 1 to 100 parts by weight per 100 parts by weight of the vinyl chloride resin, and the amount of the solvent polymerizable monomer being from 10 to 700 parts by weight per 100 parts by weight of the N-substituted maleimide. The vinyl chloride resin may if desired, be a polyvinyl chloride copolymer with a content of elastomeric resin to improve the impact resistance of the final graft copolymer. Preferably, the elastomeric resin content of the polyvinyl chloride copolymer is from 0.5 to 20% by weight. In the preparation process for the heat resistant polyvinyl chloride copolymer according to the invention, the graft polymerization may be conducted in aqueous suspension in the presence of an antioxidant, or using polyvinyl chloride resin containing an antioxidant as starting material. The product of the graft polymerization is excellent in heat resistance, particularly in Vicat softening point, and also has excellent thermal stability and processability. Furthermore, the inclusion of the elastomer content in the vinyl chloride resin gives a product having outstanding impact resistance in addition to the other excellent properties already mentioned. Consequently, the present invention is industrially very useful. The invention will now be described in more detail by way of example and with reference to the accompanying drawing in which:- Figure 1 is a graph illustrating the solubility of N-cyclohexylmaleimide in methyl methacrylate. The vinylchloride resin may be considered to be the backbone polymer of the polyvinyl chloride copolymer according to thois invention. Exemplary resins suitable for use include, for example, a homopolymer of vinyl chloride; a copolymer of vinyl chloride with a copolymerizable monomer, that is, a copolymer of vinyl chloride monomer with vinyl compounds such as α-olefins having 2 to 30 carbon atoms, acrylic acid or esters thereof, methacrylic acid or esters thereof, maleic acid or esters thereof, vinyl acetate, vinyl propionate and alkyl vinyl ether, and polyfunctional monomers such as diallyl phthalate or a mixture of the above monomers; and a graft copolymer obtained by grafting vinyl chloride monomer on ethylene/acrylic-ester copolymers such as ethylene/ethyl-acrylate copolymer, ethylene/methacrylate-ester copolymers such as ethylene/methyl-methacrylate copolymer, ethylene/vinyl-acetate copolymer (EVA), chlorinated polyethylene, butyl rubber, crosslinked acrylic rubber, polyurethane, polybutadiene/styrene/methyl-methacrylate (MBS), polybutadiene/acrylonitrile/( α - methyl)styrene (ABS), styrene/butadiene copolymer, polystyrene, polymethyl methacrylate and mixtures thereof. These resins may be used singly or in combination. Among these vinyl chloride resins, polyvinyl chloride homopolymer is particularly preferred for a heat resistant vinyl chloride resin. Particularly preferred vinyl chloride resins for a heat and impact resistant vinyl chloride resin are graft copolymers obtained by grafting vinyl chloride monomer on an elastomeric polymer such as ethylene/vinyl-acetate copolymer (EVA), chlorinated polyethylene, butyl rubber, crosslinked acrylic rubber, polyurethane, polybutadiene/styrene/methyl-methacrylate (MBS), polybutadiene/acrylonitrile/( α-methyl) styrene (ABS), styrene/butadiene copolymer or an elastomer which is a mixture of these polymers and copolymers. In these cases, the amount of elastomer contained in the graft copolymer is preferably 0.5 to 20 % by weight, more preferably 1 to 15 % by weight, and most preferably 2 to 10 % by weight, in view of the desired balance between heat resistance and impact resistance. An elastomer content less than 0.5 % by weight results in no improvement in impact resistance. An elastomer content exceeding 20 % by weight is also undesirable because of lowered heat resistance. Vinyl chloride resin for use in this invention may be prepared by suspension polymerization, bulk polymerization or emulsion polymerization. The resin may be a powder or slurry dispersed in a medium. The polymerization degree of uncrosslinked vinyl chloride resin is preferably from 300 to 5000, and more preferably from 400 to 3000. The polymerization degree of crosslinked vinyl chloride resin cannot be measured in some cases depending upon the amount of crosslinking agent. The resin is preferably polymerized in the temperature range of 30 to 80 °C. When the polymerization degree of uncrosslinked resin is less than 300, the molded product of the resin becomes brittle. A polymerization degree exceeding 5000 is undesirable due to decrease in processability. Crosslinked vinyl chloride resin polymerized at a temperature lower than 30 °C has to inferior processability, and resin obtained by polymerizing at a temperature exceeding 80 °C is also undesirable because the molded products become brittle. Exemplary N-substituted maleimides for use in this invention include, for example, aliphatic maleimides such as N-methylmaleimide, N-ethylmaleimide, N-n-propylmaleimide, N-isopropylmaleimide, N-n-butylmaleimide, N-t-butylmaleimide, N-hexylmaleimide, and N-laurylmaleimide; alicyclic maleimides such as N-cyclohexylmaleimide, and N-bicyclo-(2,2,1)-heptyl-2-methylmaleimide; aromatic maleimides such as N-phenylmaleimide, N-(o, m or p)-hydroxyphenylmaleimide, N-(o, m or p) -methoxyphenylmaleimide, N-(o, m or p)-chlorophenylmaleimide, N-(o, m or p)-carboxyphenylmaleimide, N-(o, m or p)-nitrophenylmaleimide, N-9,10-ethano-9,10-dihydroanthracenemaleimide, N-triphenylmethylbenzylmaleimide, and N-(o, m or p)-methylphenylmaleimide. These N-substituted maleimides can be used singly or in combination. Preferred N-substituted maleimides for use in the invention are N-t-butylmaleimide,N-cyclohexylmaleimide, N-phenylmaleimide and N-(o, m or p)-chlorophenylmaleimide. In the practice of this invention, the amount of N-substituted maleimide used is preferably 1 to 100 parts by weight, more preferably 2 to 80 parts by weight, and most preferably 5 to 60 parts by weight per 100 parts by weight of vinyl chloride resin. An amount of N-substituted maleimide less than 1 part by weight does not have a satisfactory effect in regard to improving heat resistance. On the other hand, an amount in excess of 100 parts by weight leads to inferior processability and makes the product unsuitable for practical use. The solvent monomer having a glass transition temperature of the polymer of 70°C or more is a monomer which acts as a solvent for the N-substituted maleimide and which provides a polymer having a glass transition temperature of 70 °C or more. More specifically, the solvent monomer for use in the present invention : (1) is liquid at the polymerization temperature of grafting the N-substituted maleimide on the vinyl chloride resin, (2) dissolves N-substituted maleimide at that temperature, and (3) in the polymer form has a glass transition temperature of 70°C or more. Illustrative solvent monomers include, for example, methacrylate esters such as methyl methacrylate, isopropyl methacrylate, t-butyl methacrylate and phenyl methacrylate; styrenes such as styrene and α-methylstyrene; and unsaturated nitriles such as acrylonitrile and methacrylonitrile. These solvent monomers can be used singly or in combination. Particularly preferred solvent monomers are methyl methacrylate, t-butyl methacrylate, phenyl methacrylate, styrene, α-methylstyrene, acrylonitrile and methacrylonitrile. The solvent monomer can also be used in combination with other monomers having a glass transition temperature of the polymer of less than 70 °C. In the case where the solvent monomer is used in combination, the composition of the solvent monomer mixture is determined so that the polymer of the mixture has a glass transition temperature of 70 °C or more in the following equation (1): 1/Tg = W₁/T₁ + W₂/T₂ + W₃/T₃ + . . . . (1) wherein Tg : glass transition temperature of the polymer of the mixture ( ° K) W₁, W₂, W₃ : portion by weight of a specific monomer in the polymer of the mixture. T₁, T₂, T₃ : glass transition temperature of homopolymer consisting of specific monomer (° K) In the practice of this invention, the solvent monomer used should be in an amount sufficient to dissolve the N-substituted maleimide at the graft polymerization temperature. The amount for use may be previously determined by conducting a dissolution test. For example, in the cases where N-cyclohexylmaleimide is used as the N-substituted maleimide and methyl methacrylate is used as the solvent monomer, the solubility is illustrated in Figure 1. When graft copolymerization is carried out at 80 °C, the methyl methacrylate may be used in an amount of 10 parts by weight or more per 90 parts by weight of N-substituted maleimide on the basis of Figure 1. In practising the polymerization, the presence of vinyl chloride resin has an effect on the amount of the solvent monomer. The amount of the solvent monomer is substantially from 10 to 700 parts by weight, preferably from 40 to 700 parts by weight, and more preferably from 100 to 600 parts by weight, per 100 parts by weight of N-substituted maleimide. An amount of the solvent monomer less than 10 parts by weight cannot completely dissolve the N-substituted maleimide and hence graft copolymerization cannot be sufficiently carried out. An amount of the solvent monomer exceeding 700 parts by weight is also undesirable because the improvement in heat resistance is not effectively achieved. The methods of graft polymerization include, for example, polymerization in the presence of a free radical yielding polymerisation catalyst or initiator, and radiation polymerization. The former is preferred. The graft copolymer can be prepared by suspension polymerization, bulk polymerization, emulsion polymerization and solution polymerization. Suspension polymerization and bulk polymerization are advantageous from the industrial and economic view points. Suspension polymerization is preferred for reasons of heat removal. Free radical-yielding initiators for use in the graft copolymerization are the common initiators used for the polymerization of vinyl chloride. Exemplary initiators include, for example, percarbonates such as diisopropylperoxy dicarbonate, dioctylperoxy dicarbonate, dilaurylperoxy dicarbonate, dimyristylperoxy dicarbonate, dicetylperoxy dicarbonate, di-tert-butylperoxy dicarbonate, di(ethoxyethyl)peroxy dicarbonate, di(methoxyisopropyl)peroxy dicarbonate, di(3-methoxybutyl)peroxy dicarbonate, di(3-methoxy-3-methylbutyl)peroxy dicarbonate, di(butoxyethyl)peroxy dicarbonate, di(2-isopropoxyethyl)peroxy dicarbonate, dibenzylperoxy dicarbonate, dicyclohexylperoxy dicarbonate, and di-t-butyl-cyclohexylperoxy dicarbonate; peresters such as tert-butyl-peroxy neodecanate, amylperoxy neodecanate, tert-octyl-peroxy neodecanate, α-cumylperoxy neodecanate, tert-butylperoxy pivalate, amylperoxy pivalate, tert-octyl-peroxy pivalate, α-cumylperoxy pivalate, perhexyl oxalate, di-tert-butylperoxy oxalate, acetylcyclohexylsulfonyl peroxide, and 1,1,3,3-tetramethylbutylperoxyphenoxy acetate; diacyl peroxides such as lauroyl peroxide, diisobutyl peroxide, 2-ethylhexanoyl peroxide, and 3,5,5-trimethylhexanoyl peroxide; azo compounds such as 2,2-azobis-isobutyronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, and 2,2′-azobis-4-methoxy-2,4-dimethylvaleronitrile, water soluble peroxides such as potassium persulfate and ammonium persulfate; and water soluble azo compounds such as 2,2′-azobis(2-aminopropane) hydrochloride, and 2,2′-azobis(N,N′-dimethyleneisobutylamidin) hydrochloride. Such free radical-yielding initiators may be used in combination in order to obtain a uniform rate of polymerization. The initiator is preferably used in an amount of 0.005 to 20.0 parts by weight per 100 parts by weight of the sum of N-substituted maleimide and the solvent monomer. The polyvinyl chloride copolymers of this invention are superior in heat resistance to a blend of vinyl chloride resin and the copolymer of N-substituted maleimide/solvent monomer which are the constituent components of the copolymer of this invention. The reason is not clear, but the following process is assumed to proceed. As a result of the graft copolymerization the resultant polyvinyl chloride copolymer contains vinyl chloride resin ( I ) , copolymer obtained by grafting N-substituted maleimide and solvent monomer on vinyl chloride resin(II ), and copolymer of N-substituted maleimide/solvent monomer (III ). II functions as a high molecular compatibilizer of I and III and leads to a mixture of I, II and III in a micro-structure. In actual viscoelasticity measurement, the heat resistant polyvinyl chloride copolymer of this invention exhibits completely or almost mixed peak patterns. On the other hand, a blended product exhibits almost separated or only slightly mixed peak patterns. On account of the difference in such property, the copolymer of this invention has excellent heat resistance and high thermal stability. In aqueous suspension polymerization, the weight ratio of the amount of the sum of vinyl chloride resin, N-substituted maleimide and solvent monomer to the amount of water is preferably from 1 : 0.8 to 1 : 10, and more preferably from 1 : 1 to 1 : 4. When the proportion of water to the sum of vinyl chloride resin, N-substituted maleimide and solvent monomer is less than 0.8, the aqueous suspension increases in viscosity to the point at which it is difficult to stir. On the other hand, at a proportion exceeding 10 the productivity is decreased to the point at which it is industrially and economically disadvantageous. A suspension stabilising agent may be used in the suspension polymerization if necessary. Examples of suspension stabilising agents that may be mentioned are polyvinyl alcohols, cellulose derivatives, maleic-anhydride/styrene copolymer, maleic-anhydride/methyl-vinyl-ether copolymer, polyvinyl pyrrolidone and gelatin. These agents may be used singly or in combination. Emulsifiers may be added if desired. The amount of the suspension stabilising agent should be less than 1.0 part by weight per 100 parts by weight of vinyl chloride resin and preferably in the range from 0.02 to 1.0 parts by weight. Chain transfer agents as used in the conventional polymerization of vinyl compounds may be employed for the graft polymerization of this invention if desired. Exemplary chain transfer agents suitable for use include, for example, chlorinated aliphatic hydrocarbons such as carbon tetrachloride, chloroform, methylene chloride, butyl chloride, methylchloroform, propylene chloride and trichloroethylene; aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene, ethylbenzene, t-butylbenzene and chlorobenzene; aldehydes such as acetaldehyde, propionaldehyde, benzaldehyde and crotonaldehyde; aliphatic and cyclic ketones such as methyl ethyl ketone, acetone, diethyl ketone, methyl isobutyl ketone and cyclohexanone ethyl ketone; cyclic ethers such as dioxane and tetrahydrofuran; aliphatic carboxylic acid alkyl esters such as methyl isobutyrate and ethyl acetate; aliphatic alcohols such as sec-butyl alcohol, n-butyl alcohol, isobutyl alcohol and t-butyl alcohol; aliphatic carboxylic acids such as acetic acid; and cyclic hydrocarbons such as methylcyclohexane. Exemplary chain transfer agents suitable for use in this invention further include, for example, monoalkyl mercaptans such as methyl mercaptan, ethyl mercaptan, propyl mercaptan, n-and t-butyl mercaptan, hexyl mercaptan, n-and t-heptyl mercaptan, n-and t-octyl mercaptan, n-and t-dodecyl mercaptan, n-and t-tetradecyl mercaptan, n-and t-hexadecyl mercaptan, n-and t-pentacosyl mercaptan,n-and t-octacosyl mercaptan, n-and t-triconyl mercaptan and mono-,di-and tri-mercaptans containing a mixture of these mercaptans. Illustrative examples of other effective monomercaptans are, for example, thioacetic acid, 1-mercapto-2-butanone, methyl mercaptoacetate, ethyl mercaptothioacetate, 1-mercapto-2-ethoxyethane, diethyl mercaptoethylphosphortrithioate, 2-mercaptoethylacetamide, dimethylaminomethylmercaptan, cysteamine, mercaptomethylthiopropane, monomercaptocyclohexane, benzyl mercaptan, cystein and mercaptoethanol. Illustrative examples of dimercaptan chain transfer agents are ethanedithiol, 2,3-dimercaptopropanol and decane-1,10-dithiol. Exemplary suitable polymercaptan chain transfer agents having three or more mercaptan groups in the molecule include, for example, pentaerythritol tetra (7-mercaptoheptanoate), glycerol tri(mercapto-acetate), pentaerythritol tri (β-mercaptopropionate), pentaerythritol tetra(β-mercaptopropionate), cellulose tri(α-mercaptoacetate),1,2,3-propanetrithiol, 1,2,3,4-neopentanetetrathiol, 1,2,3,4,5,6-mercaptopoly(ethyleneoxy)ethyl(sorbitol), 1,1,1-trimethylpropane tri(α-mercaptoacetate), dipentaerythritolhexane(3-mercaptopropionate), 1,2,3-tri(α-mercaptoacetyl)propane, thiopentaerythritol tetra(α-mercaptoaceate), 1,6,10-trimercapto-cyclododecan, 1,2,3,4,5,6-hexamercapto-cyclohexane, N,N′,N″,N‴-tetra(2-mercaptoethyl)pyromellitic amide, tri(2-mercaptoethyl)nitrilo triacetate, pentaerythritol tetra(α-mercaptoacetate), tri(p-mercaptoethylphenyl)methane, 2,2,7,7-tetrakis (mercaptomethyl)-4,5-dimercapto-octane, 5,5,5-tri(mercaptoethyl)phosphorotrithioate and xylitol penta(β-mercaptopropionate). Exemplary chain transfer agents of low molecular weight polymer having three or more mercapto groups in the molecule are, for example, homopolymers and copolymers of vinyl thiols such as polyvinyl thiol. Other polymer thiols such as glycerol/ethylene glycol polyether polymercaptan can also be used as chain transfer agents in the process of this invention. These chain transfer agents may be used singly or in combination. The amount of chain transfer agent to be used in the process of this invention is determined by the specific type of chain transfer agent selected. The amount, however, will generally be 10 parts by weight or less per 100 parts by weight of the sum of N-substituted maleimide and solvent monomer. Chain transfer agents such as mercaptans and particularly polymercaptans are generally most effective and may therefore be used in small concentrations. On the other hand, chain transfer agents such as aromatic hydrocarbon base transfer agents having a lesser effect need to be used in a concentration around the foregoing upper limit. Compounds having a swelling action upon vinyl chloride resin, for example, ketones such as acetone and methyl ethyl ketone, may be used, in order to increase grafting efficiency, in a range giving no adverse effect on the attainment of the object of this invention, if desired. Antioxidants are preferably added to the graft copolymers of this invention in order to enhance thermal stability. Exemplary antioxidants suitable for use may be mentioned, for example, phenolic antioxidants such as 2,6-di-t-butyl-p-cresol(DBT), 3-t-butyl-4-hydroxyanisole(3-BHT), 2-t-butyl-4-hydroxyanisole(2-BHT), 2,2-methylenebis(4-methyl-6-t-butylphenol)(MBMBP), 2,2-methylenebis(4-ethyl-6-t-butylphenol)(MBEBP), 4,4′-butylidenebis(3-methyl-6-t-butylphenol)(BBMDP), styrenated phenol, styrenated-p-cresol, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenol)butane, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenol propionate]-methane, n-octadecyl-3-(4-hydroxy-3-,5-di-t-butylphenyl)propionate, triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxy-phenyl)-propionate], 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)benzene, 2,2′-dihydroxy-3,3′-di(α-methylcyclohexyl)-5,5′-dimethyldiphenyl methane, 4,4-methylenebis(2,6-di-t-butylphenol), tris(3,5-di-t-butyl-4-hydroxyphenyl) isocyanurate, 1,3,5-tris(3′,5′-di-t-butyl-4-hydroxybenzoyl) isocyanurate, bis[2-methyl-4-(3-n-alkylthiopropionyloxy)-5-t-butylphenyl] sulfide, 1-oxy-3-methylisopropylbenzene, 2,5-dibutylhydroquinone, 2,2′-methylenebis(4-methyl-6-nonylphenol), alkylated bisphenol, 2,5-di-t-amylhydroquinone, polybutylated bisphenol-A, bisphenol-A, 2,6-di-t-butyl-p-ethylphenol, 2,6-bis(2′-hydroxy-3-t-butyl-5′-methylbenzyl)-4-methylphenol, 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate, terephthaloyl-di(2,6-dimethyl-4-t-butyl-3-hydroxybenzyl sulfide), 2,6-di-t-butylphenol, 2,6-di-t-butyl-2-dimethylamino-p-cresol, 2,2′-methylenebis(4-methyl-6-cyclohexylphenol), hexamethylene glycol bis(3,5-t-butyl-4-hydroxyphenyl) propionate, 6-(4-hydroxy-3,5-di-t-butylanilino)-2,6-bis(octylthio)-1,3,5-triazine, 2,2-thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], N,N′-hexamethylenebis(3,5-di-t-butyl-4-hydroxycinnamide), 3,5-di-t-butyl-4-hydroxybenzylphosphoric acid diethyl ester, 2,4-dimethyl-6-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-thiobis(2-methyl-6-t-butylphenol), tris[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate, 2,4,6-tributylphenol, bis[3,3-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester, 4-hydroxymethyl-2,6-di-t-butylphenol, and bis(3-methyl-4-hydroxy-5-t-butylbenzyl) sulfide; amine antioxidants such as N-phenyl-N′-isopropyl-p-phenylenediamine, N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine, N,N′-diphenyl-p-phenylenediamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer and diaryl-p-phenylenediamine; sulfur containing antioxidants such as dilauryl thiodipropionate, distearyl thiodipropionate and 2-mercaptobenzimidazol; and phosphorus containing anti-oxidants such as distearylpentaerythritol diphosphite. Antioxidants other than those set forth above can also be used for this invention. The antioxidants can be used singly or in combination. The antioxidants may be added to the graft-polymerized copolymer. However, the antioxidants are more preferably contained in the vinyl chloride resin to be used for the raw material or added in the graft polymerization step, which method markedly improves the thermal stability of the resulting copolymer. The antioxidants may be added before or during polymerization. The amount of antioxidant contained in the vinyl chloride resin to be used for graft copolymerization or added in the step of graft polymerization is preferably in the range of from 5 to 500 ppm by weight, more preferably from 5 to 200 ppm by weight, and most preferably from 5 to 100 ppm by weight. When the amount of antioxidant contained in the vinyl chloride resin or added in the graft polymerization step is less than 5 ppm by weight, thermal stability of the grafted copolymer is unsatisfactory. On the other hand, an amount exceeding 500 ppm by weight inhibits completion of the polymerization reaction or necessitates use of a larger amount of the free radical-yielding initiator, which causes an adverse effect on the thermal stability of the resulting graft copolymer. The temperature of the graft copolymerization is preferably from 30 to 100°C and more preferably from 40 to 100 °C. A reaction temperature lower than 30 °C serves to slow down the rate of graft polymerization and is hence industrially and economically undesirable. On the other hand, a reaction temperature above 100 °C leads to deterioration of the vinyl chloride resin. The reaction temperature may be varied during the course of the reaction. In particular when the polymerization is carried out at a lower temperature the reaction temperature may be raised in the latter half of the reaction time in order to decrease unreacted monomer. Reaction time is determined by the type and amount of free radical-yielding initiator used and the reaction temperature and is preferably adjusted to complete the grafting reaction in 1 to 15 hours. The reaction vessel for use in graft copolymerization is preferably a stainless steel or glass lined autoclave equipped with a stirrer and jacket. The reaction vessel may also have a reflux condenser as auxiliary equipment for heat removal. In the interior of the reaction vessel, the oxygen content of the atmosphere must be reduced to a level giving no adverse effect on the polymerization. On conducting the graft copolymerization, the N-substituted maleimide, solvent monomer, free radical-yielding initiator, suspension stabilizer, chain transfer agent, swelling agent and antioxidant may be charged, if desired, all at once, portion by portion or continuously. After completion of the graft copolymerization, unreacted monomer is removed by a usual procedure. The residual slurry is dehydrated and dried. The graft copolymer obtained by the process of this invention can have any of the usual additives included, such as heat stabilizers, light stabilizers, lubricants, fillers, colorants, impact resistance improvers and heat resistance improvers, of the kinds which are commonly used in the processing of vinyl chloride resins. Further possible additives are processing aids, flame retardants and smoke inhibitors, such as are generally employed in vinyl chloride resins, included in a range leading to no adverse effect on the attainment of the object of this invention. A broad range of known stabilizers can be employed in the processing of the graft copolymer of this invention. However, the stabilizers that can be used are not limited to such known stabilizers. Illustrative heat stabilizers include, for example, lead stabilizers such as white lead, tribasic lead sulfate, dibasic lead phosphite, dibasic lead phthalate, dibasic lead maleate, lead silicate and co-precipitated lead silicate with silica gel; metal soaps such as magnesium soap, calcium soap, barium soap, cadmium soap, zinc soap, lead soap and tin soap; liquid stabilizers such as cadmium-barium base, cadmium-barium-zinc base and barium-zinc base; organotin stabilizers such as alkyltin sulfide, aryltin sulfide, alkyltin oxide, aryltin oxide, organotin carboxylic acid and organotin mercaptide; epoxy stabilizers such as glycidyl ether and epoxy resin, epoxylated fats and oils, alkyl esters of epoxylated natural fatty acids and resin acids, and epoxy derivatives of cyclohexane; organic phosphites such as trialkyl phosphite, triphenyl phosphite and triallyl phosphite; polyhydric alcohols; and amine compounds. Exemplary light stabilizers include, for example ultra-violet absorbers such as salicylate esters, benzoate esters, benzophenone derivatives, benzotriazole derivatives and acrylonitrile derivatives; ultra-violet stabilizers such as phosphorus compounds; and titanium oxide. Suitable lubricants may be mentioned, for example, metal soaps such as magnesium stearate, calcium stearate, barium stearate, zinc stearate, and lead stearate; hydrocarbons such as liquid paraffin, natural paraffin, polyethylene wax, chlorinated hydrocarbon and fluorocarbon; fatty acids such as stearic acid, behenic acid, arachidic acid and oxy fatty acid; fatty acid amides such as fatty acid amide and alkylenebis fatty acid amide; fatty acid esters such as lower alcohol esters of fatty acids, polyglycol esters of fatty acids and aliphatic alcohol esters of fatty acids; polyhydric alcohols, polyglycols and polyglycerols; partial esters of polyhydric alcohols with fatty acids; partial esters of polyglycols with fatty acids; and partial esters of polyglycerols with fatty acids. Illustrative fillers include, for example, calcium carbonate, clay, hydrated silicate, silica, calcium silicate, aluminum silicate, asbestos, antimony oxide, talc, trihydrated aluminum, hydated zinc borate, magnesia, sodium bicarbonate, potassium nitrate, calcium hydroxide, mica and synthetic fluoro mica. Exemplary colorants may be mentioned, for example, organic pigments and inorganic pigments. Organic pigments include azopigments such as azo lake, insoluble azo pigments and condensation azo pigments; phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green; vat dye pigments such as anthroquinone pigments, perylene pigments, thioindigo pigments and isoindoline pigments; dyeing lake pigments such as basis dye lake and acid dye lake; quinacrydone pigments and dioxadine pigments. Inorganic pigments include precipitated pigments such as chromate, molybdate, oxide and cyanide; precipitated and calcined pigments such as oxide pigments and sulfide pigments; calcined pigments such as oxide pigments, ultramarine blue and cobalt blue; metal powders and pearl pigment. Illustrative impact resistance improvers include, for example, ethylene-vinyl acetate copolymer (EVA), ethylene-propylene copolymer (EPR), polybutadiene-acrylonitrile-styrene copolymer (ABS), polybutadiene-styrene-methyl methacrylate (MBS), polybutylacrylate, crosslinked acrylic rubber, styrene-butadiene copolymer (SBR) and acrylonitrile-butadiene copolymer (NBR). Exemplary heat resistance improvers include, for example, acrylonitril- α-methylstyrene-butadiene copoymer and polymethyl methacrylate-acrylic ester copolymer. The present invention will be further explained with reference to the following examples. In the following examples and comparative examples, the below described additives were included in the amounts given for 100 parts by weight of the graft copolymer. Tribasic lead sulfate 2 parts by weight Dibasic lead stearate 1 part by weight Lead stearate 1 part by weight Stearic acid 0.5 part by weight Calcium stearate 0.3 part by weight In these examples, the copolymer and additives were mixed in a Henschel mixer and extruded with a 30 mm anisotropic twin-screw extruder to form a joint plate having a thickness of 3 mm and a width of 40 mm. The properties were evaluated by the following methods. (a) Vicat softening points were measured under 5 kgf load in accordance with JIS K-7206. (b) Thermal stability was indicated by the time required to generate a black discoloration in a Geer's oven at 190 °C. (c) Processability was divided into the following four classes by observing the surface appearance of the joint plate. o ○ Surface is smooth and no flash is found at the edge. ○ Surface is smooth and small flashes are found at the edge. ▵ Surface is slightly rough and flashes are found at the edge. × Surface is rough and large flashes are found. The determination of the antioxidant to be contained in the polyvinyl chloride resin for use in the graft copolymer was carried out by gas chromatography or liquid chromatography. Example 1 A stainless steel autoclave having an internal volume of 840ℓ and equipped with a stirrer and a jacket was charged with 100 kg of suspension polymerized polyvinyl chloride resin having a polymerization degree of 1050 and containing 10 ppm by weight of bisphenol A and 354 kg of deionized water. Separately, 10 kg of N-cyclohexyl-maleimide, 30 kg of methyl methacrylate and 0.40 kg of azobisisobutyronitrile were mixed. The weight ratio of these ingredients in the mixture corresponded to 1 part by weight of azobisisobutyronitrile per 100 parts by weight of the sum of N-substituted maleimide and solvent monomer. The air in the interior of the autoclave was evacuated with a vacuum pump and the mixture was sucked into the autoclave. Subsequently, the reaction was carried out at 80°C for 6 hours. The reaction product was dehydrated and dried to obtain 117 kg of graft copolymer. The copolymer thus obtained was extruded to form a joint plate by the same procedure as described above and its properties were evaluated. The results are given in Table 1. Example 2 A stainless steel autoclave having an internal volume of 840ℓ and equipped with a stirrer and a jacket was charged with 100 kg of suspension polymerized polyvinyl chloride resin having a polymerization degree of 1050 and 354 kg of deionized water. Separately, 10 kg of N-cyclohexyl-maleimide, 30 kg of methyl methacrylate and 0.40 kg of azobisisobutyronitrile were mixed. The air in the interior of the autoclave was evacuated with a vacuum pump and the mixture was sucked into the autoclave. Subsequently, the reaction was carried out at 80°C for 6 hours. The reaction product was dehydrated and dried to obtain 117 kg of graft copolymer. The copolymer thus obtained was extruded to form a joint plate by the same procedure as described above and its properties were evaluated. The results are given in Table 1. Example 3 The same procedures as described in Example 1 were carried out except that polyvinyl chloride resin containing 200 ppm by weight of Irganox (Registered Trade Mark) 1076 (a product of Ciba Geigy Ltd.) was used in place of polyvinyl chloride resin containing 10 ppm by weight of bisphenol-A, and 4 kg of azobisisobutyronitrile was used. The graft copolymer obtained was extruded to form a joint plate by the same procedure as described above. The results on evaluation are given in Table 1. Comparative Example 1 A stainless steel autoclave having an internal volume of 840ℓ and equipped with a stirrer and a jacket was charged with 100 kg of suspension polymerized polyvinyl chloride resin having a polymerization degree of 1050 and containing 10 ppm by weight of bisphenol-A and 354 kg of deionized water. Separately, 8 kg of deionized water, 10 kg of N-cyclohexylmaleimide and 0.16 kg of azobisisobutyronitrile were mixed. The air in the interior of the autoclave was evacuated with a vacuum pump and the mixture above was sucked into the autoclave. Stirring was started and the reaction was carried out at 80°C for 6 hours. The reaction product was dehydrated and dried to obtain 107 kg of graft copolymer. The product was yellow colored. An attempt was made to form a joint plate with the copolymer by the same procedure as described above. However, the copolymer generated a bad smell and caused eye irritation. Consequently, the extruding operation was abandoned. The result is given in Table 1. Comparative Example 2 Suspension polymerized polyvinyl chloride resin having a polymerization degree of 1050 and containing 10 ppm by weight of bisphenol A was subjected by itself to an extruding operation. The results on evaluation are given in Table 1. Comparative Example 3 A stainless steel autoclave having an internal volume of 840ℓ and equipped with a stirrer and a jacket was charged with 310 kg of deionized water, 105 g of a 70 % by weight solution of 2-ethyl-hexylperoxy dicarbonate and 5 kg of N-cyclohexylmaleimide. After evacuating the air in the interior of the autoclave with a vacuum pump, 8.4 kg of a 5 % by weight aqueous solution of partially saponified polyvinyl alcohol having a saponification degree of 80 mole % and a polymerization degree of about 2000 and 120 kg of vinyl chloride monomer were added. The reaction was carried out at 57°C. A dispersion of 5 kg of N-cyclohexylmaleimide in 30 kg of a deionized water solution containing 30 g of the above partially saponified polvinyl alcohol was charged into the autoclave after 2.5 hours at increased pressure. When the internal pressure of the autoclave was lowered to 6.5 kg/cm²G, the unreacted monomer was recovered. The slurry was dehydrated and dried to obtain 110 kg of copolymer as a white powder. The results of evaluation conducted as in Example 1 are given in Table 1. Reference Example 1 A stainless steel autoclave having an internal volume of 840ℓ and equipped with a stirrer and a jacket was charged with 252 kg of deionized water, 12.5 kg of N-cyclohexylmaleimide, 25 g of partially saponified polyvinyl alcohol having a saponification degree of 80 % by mole and a polymerization degree of about 2000 and 150 g of lauroyl peroxide. After evacuating the air in the interior of the autoclave with a vacuum pump, 37.5 kg of methyl methacrylate were added with stirring and polymerization was carried out at 80 °C for 6 1/4 hours. The resulting slurry was dehydrated and 47.5 kg. of dried white powder were obtained. Comparative Example 4 A blend of 100 kg of the suspension polymerized polyvinyl chloride resin of Comparative Example 2, having a polymerization degree of 1050, and 40 kg of N-cyclohexylmaleimide/methyl methacrylate copolymer was extruded to form a joint plate by the same procedure as described above. The results on evaluation are given in Table 1. Comparative Example 5 The same procedures as described in Example 1 were carried out except that polyvinyl chloride resin containing 100 ppm by weight of bisphenol-A and 500 ppm by weight of Irganox 1076 was used in place of polyvinyl chloride resin containing 10 ppm by weight of bisphenol-A; and 10 kg of azobisisobutyronitrile was used in place of 0.40kg of azobisisobutyronitrile. The graft copolymer obtained was extruded to form a joint plate by the same procedure as described above. The copolymer generated a bad smell and caused eye irritation during extrusion. The results on evaluation are given in Table 1. Examples 4-17 Graft copolymers were prepared by carrying out the same procedures as described in Example 1 except that various N-substituted maleimides as set out in Table 2 were used in place of N-cyclohexyl-maleimide. The copolymers obtained were extruded to form joint plates by the same procedure as described above. The results on evaluation are given in Table 2. Examples 18-21 and Comparative Examples 6 and 7 The same procedures as described in Example 1 were carried out except that the amounts of N-cyclohexyl-maleimide and methyl methacrylate were varied as set out in Table 3 and azobisisobutyronitrile was used in an amount of 1 part by weight per 100 parts by weight of the sum of N-cyclohexylmaleimide and methylmethacrylate. The graft copolymers obtained were extruded to form joint sheets by the same procedure as described above. The results on evaluation are given in Table 3. Examples 22 and 23 and Comparative Example 8 The same procedures as described in Example 1 were carried out except that solvent monomers as set out in Table 4 were used in place of methyl methacrylate. The graft copolymers obtained were extruded by the same procedure as described above. The results on evaluation are given in Table 4. Examples 24 to 27 and Comparative Example 9 and 10 The same procedures as described in Example 1 were carried out except that the amount of the solvent monomer was varied as set out in Table 4 and azobisisobutyronitrile was used in an amount of 1 part by weight per 100 parts by weight of the sum of N-cyclohexylmaleimide and methyl methacrylate. The graft copolymers obtained were extruded by the same procedure as described above. The results on evaluation are given in Table 4. Reference Example 2 (Preparation Example of crosslinked acrylic rubber) A 5 m³ stainless steel autoclave equipped with a stirrer and a jacket was charged with 2000 kg of deionized water, 7.0 kg of anionic emulsifier, 0.67 kg of ammonium per-sulphate,700 kg of n-butyl methacrylate and 31 kg of 1,3-butylene glycol diacrylate. After replacing the air with nitrogen in the interior of the autoclave, polymerisation was carried out at 60 °C. Rapid increase in the reaction temperature occurred after 16 hours from the start of the reaction, and water was passed through the jacket to remove generated heat. The polymerization was terminated after being conducted for a further 10 hours at the same temperature. The latex thus obtained had a concentration of 25 % by weight and an average particle size of 0.07 µm. Reference Example 3 (Preparation Example of rubber containing graft copolymer) A stainless steel autoclave having an internal volume of 7 m³ and equipped with a stirrer and a jacket was charged with 2700 kg of deionized water, 1.5 kg of partially saponified polyvinyl alcohol having a saponification degree of 80 % by mole and a polymerisation degree of about 2000, 1.4 kg of methyl cellulose, 0.17 kg of 2,2'-azobisisobutyronitrile and 0.29 kg of 2,2'-azobis-2,4-dimethylvaleronitrile. After evacuating the air in the interior of the autoclave with a vacuum pump, 368 kg (92 kg as solid ingredient) of the acrylic latex having a concentration of 25 % by weight which was obtained in Reference Example 2 was added with stirring and coagulated, and thereafter 1400 kg of vinyl chloride was added and polymerization carried out at 57°C. The internal pressure of the autoclave decreased to 6.5 kg/cm²G with the progress of polymerization. Then 25 g of bisphenol-A was added to terminate polymerization. After removing unreacted vinylchloride, the resulting slurry was dehydrated and dried. 1282 kg of white powder was obtained containing 7.2 % by weight of rubber ingredient on the basis of chlorine analysis. Reference Example 4 A polymerization reaction was carried out by the same procedures as described in Reference Example 3 except that, after charging the deionized water, 92 kg of EVA containing 45 % by weight of vinyl acetate was added in place of 368 kg (92 kg as solid ingredient) of the acrylic latex. 1280 kg of white powder was obtained containing 7.2 % by weight of rubber ingredient on the basis of chlorine analysis. Example 28 A graft copolymer was prepared by carrying out the same procedures as described in Example 1 except that the polyvinyl chloride resin product obtained in Reference Example 3 was used in place of the suspension polymerized polyvinyl chloride resin containing 10 ppm by weight of bisphenol-A and having a polymerization degree of 1050. A joint plate was extruded from the graft copolymer by the same procedure as described above. The results on evaluation are given in Table 5. Sharpy impact strength was measured by using a hammer having a moment of 60 kgf-cm in accordance with JIS K-6754. Example 29 A graft copolymer was prepared by carrying out the same procedures as described in Example 1 except that the polyvinyl chloride resin product obtained in Reference Example 4 was used in place of the suspension polymerized polyvinyl chloride resin containing 10 ppm by weight of bisphenol-A. A joint plate was extruded from the graft copolymer by the same procedure as described above. The results on evaluation are given in Table 5. Reference Example 5 After carrying out the same procedures as described in Reference Example 3, the polymerization reaction was terminated by the addition of 125 g of bisphenol-A and 650 g of Irganox 1076 in place of 25 g of bisphenol-A. 1283 kg of a white powder was obtained containing 7.2 % by weight of rubber ingredient on the basis of chlorine analysis. Comparative Example 11 A graft copolymer was prepared by carrying out the same procedures as described in Example 1 except that the polyvinyl chloride resin product obtained in Reference Example 5 was used in place of the polyvinyl chloride resin containing 10 ppm by weight of bisphenol-A and 10 kg of azobisisobutyronitrile was used in place of 0.40 kg of azobisisobutyronitrile. A joint plate was extruded from the graft copolymer by the same procedure as described above. The graft copolymer generated a bad smell and caused eye irritation during the extrusion operation. - The results on evaluation are given in Table 5. Example No. Vicat softening point (°C) Thermal stability (min) Processability Sharpy impact strength (kgf cm/cm²) Ex. 1 96 240 o ○ 5 Ex. 22 94 240 o ○ 4 Ex. 28 94 240 o ○ 19 Ex. 29 94 240 o ○ 14 Comparat. Ex. 11 89 170 × 6

Claims: A process for the preparation of a heat resistant polyvinyl chloride copolymer by graft copolymerization of an N-substituted maleimide on a vinyl chloride resin, which comprises conducting the graft copolymerisation in the presence of a solvent polymerizable monomer which: (1) is a liquid at the polymerization temperature, (2) is capable of dissolving the N-substituted maleimide at that temperature, (3) has a glass transition temperature in the polymer state of at least 70°C, and (4) is used in an amount sufficient to dissolve the N-substituted maleimide, the amount of N-substituted maleimide being from 1 to 100 parts by weight per 100 parts by weight of the vinyl chloride resin, and the amount of the solvent polymerizable monomer being from 10 to 700 parts by weight per 100 parts by weight of the N-substituted maleimide. A process as claimed in Claim 1 in which the vinyl chloride resin is a homopolymer of vinyl chloride. A process as claimed in Claim 1 in which the vinyl chloride resin is an elastomer-containing polyvinyl chloride copolymer. A process as claimed in Claim 3 in which the elastomer content of the elastomer-containing polyvinyl chloride copolymer is from 0.5 to 20% by weight. A process as claimed in any preceding claim in which the vinyl chloride resin contains an antioxidant in an amount of 5 to 500 ppm by weight. A process as claimed in Claim 5 in which the antioxidant is added to the graft copolymerization mix in an amount of 5 to 500 ppm by weight based on the vinyl chloride resin. A process as claimed in any preceding claim in which the N-substituted maleimide is N-t-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide or N-(o,m or p)-chlorophenylmaleimide. A process as claimed in any preceding claim in which the solvent polymerizable monomer is methyl methacrylate, t-butyl methacrylate, isopropyl methacrylate phenyl methacrylate, styrene, α-methylstyrene, acrylonitrile or methacrylonitrile. A process as claimed in any preceding claim in which the graft copolymerization is conducted in the presence of a free radical-yielding polymerization initiator. A process as claimed in Claim 9 in which the graft copolymerization is carried out in suspension or in bulk. A process as claimed in Claim 9 in which the graft copolymerization is carried out in aqueous suspension.

Inventors: MASUKO SEIICHI, TAKAHARA HIDEAKI, YAMAMOTO AKIRA, MASUKO, SEIICHI, TAKAHARA, HIDEAKI, YAMAMOTO, AKIRA
Applicants: MITSUI TOATSU CHEMICALS, MITSUI TOATSU CHEMICALS, INC.
Application year: 1989
Main classification: C08F259
IPC codes: C08F259