POLYACETAL RESIN COMPOSITIONS HAVING IMPROVED RESISTANCE TO DETERIORATION WHEN EXPOSED TO LIGHT AND CONTAINING ALKYLIDENE BIS(BENZOTRIAZOLYL PHENOLS)

Abstract: Polyacetal resin compositions are provided having im­ proved light stability and comprising an alkylidene bis(ben­ zotriazolyl phenol) having the formula: wherein: R₁ is selected from the group consisting of hydrogen and alkyl having from one to about eleven carbon atoms; R₂ is selected from the group consisting of alkyl having from one to about twelve carbon atoms; and arylalkyl having from seven to about eighteen carbon atoms; and X is selected from the group consisting of hydrogen; halogen; alkyl having from one to about twelve carbon atoms; aryl alkyl having from seven to about eighteen carbon atoms; alkoxy having from one to about twelve carbon atoms; phenoxy; arylalkoxy having from seven to about eighteen carbon atoms; and phenyl.

Description: Polyacetal resins undergo a decrease in mechanical strength and an increase in color when exposed to ultraviolet light. Light stabilizers accordingly are added to improve the resistance of the polyacetal resin to such deterioration, of which the benzotriazole type are used most frequently. However, the available benzotriazoles are not as effective as would be desired. US-A-3,936,305 discloses that compounds represented by the following general formula are extremely effective as ultraviolet ray-absorbing agents, especially for color photographic photosensitive materials: wherein R₁ is an alkyl group having 1 to 13, preferably 5 to 13 carbon atoms, R₂ is an alkyl group having 1 to 18 carbon atoms and X is hydrogen, a halogen, an alkyl, an alkoxy, an aryloxy, an aralkyloxy or an aryl group. The patentees note that hydroxy benzotriazole is known as an excellent ultraviolet ray-absorbing agent, but gives solubility problems, crystallizing out in the amounts needed for adequate protection. The alkylidene-bis-benzotriazolylphenols are more soluble, and in addition cause no discoloration and are not colored themselves, when used in photosensitive gelatin or other hydrophilic protective colloid compositions. 2,2'-Methylene-bis-(4-hydrocarbyl-6-benzotriazolyl-phenols) are known light stabilizers for plastics, and a process for preparing them is disclosed in Chemical Abstracts 74 53666f (1971) and 77 62720h (1972). DE-A-16 70 951 discloses, among others, compounds of the above general formula and it is stated therein that said compounds are suitable, particularly, as UV-absorbers for polymers. From EP-A-15230 it is known that mono-benzotriazole compounds are useful as UV-absorbers in polymers, including polyacetals. In accordance with this invention, polyacetal resin compositions are provided having improved light stability and comprising an alkylidene bis(benzotriazolyl phenol) having the formula: wherein: R₁ is selected from hydrogen and alkyl having from one to eleven carbon atoms; R₂ is selected from alkyl having from one to twelve carbon atoms; and arylalkyl having from seven to eighteen carbon atoms; and X is selected from hydrogen; halogen; alkyl having from one to twelve carbon atoms; aryl alkyl having from seven to eighteen carbon atoms; alkoxy having from one to twelve carbon atoms; phenoxy; arylalkoxy having from seven to eighteen carbon atoms; and phenyl; as well as 0.001 to 3 parts by weight per 100 parts by weight of polyacetal resin of a polycyclic phenolic antioxidant specified hereinbelow. Exemplary R₁ alkyl include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl, isoamyl, tert-amyl, hexyl, isohexyl, sec-hexyl, heptyl, sec-heptyl, tert-heptyl, isoheptyl, octyl, isooctyl, sec-octyl, tert-octyl, 2-ethylhexyl, nonyl, isononyl, tert nonyl, decyl, isodecyl and undecyl; Exemplary R₂ and X alkyl include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl, amyl, isoamyl, t-amyl, hexyl, isohexyl, tert-hexyl, octyl, 2-ethylhexyl, isooctyl, 1,1,3,3-tetramethylbutyl, nonyl, isononyl, tert-nonyl, decyl, isodecyl and dodecyl; Exemplary R₂ and X arylalkyl include benzyl, α-methylbenzyl, mesityl, xylyl, and cumyl; Exemplary X halogen include chlorine, bromine, iodine and fluorine; Exemplary X alkoxy and arylalkoxy include methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, amyloxy, isoamyloxy, sec-amyloxy, tert-amyloxy, hexoxy, isohexoxy, heptoxy, isoheptoxy, octyloxy, isooctyloxy, 2-ethylhexoxy, tert-octyloxy, nonyloxy, isononyloxy, decyloxy, isodecyloxy, undecyloxy, and dodecyloxy; benzyloxy, xylyloxy, 2-methylbenzyloxy, cumyloxy, mesityloxy and xylyloxy. Preferred alkylidene bis(benzotriazolyl phenols) falling within the invention include: 2,2'-methylenebis(4-methyl-6-benzotriazolyl phenol) 2,2'-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolyl phenol) 2,2'-methylenebis(4-cumyl-6-benzotriazolyl phenol) 2,2'-octylidenebis(4-methyl-(5'-methylbenzotriazolyl) phenol) 2,2'-octylidenebis(4-methyl-(5'-chlorobenzotriazolyl) phenol). The alkylidene-bis-benzotriolyl-phenols can be prepared by: (1) reacting a 4-hydrocarbyl-6-benzotriazolyl phenol having the formula I: with an amine HNR₁R₂ and formaldehyde in an organic solvent to produce a Mannich base having formula II: and (2) reacting the Mannich base with itself or a 4-hydrocarbyl-6-benzotriazolyl phenol having formula I, thereby forming a 2,2'-methylene-bis-(4-hydrocarbyl-6-benzotriazolyl-phenol. The following Examples represent preferred embodiments of the process. Example 1 Preparation of 2,2¹-methylene-bis-(4-methyl-6-benzotriazolyl-phenol ) 4-Methyl-6-benzotriazolyl-phenol 226 g, diethylamine 110 g, and paraformaldehyde 51.8 g were dissolved in 250 ml of butanol, and heated with stirring at reflux temperature (95°C to 105°C) for 24 hours. The solvent was vacuum distilled off, and 308 g of 2-diethylaminomethyl-4-methyl-6-benzotriazolyl-phenol Mannich base was obtained as residue. (Yield = 99%) This Mannich base, 7.8 g, was dissolved in 20 ml of xylene, and sodium methylate (28% methanol solution) 0.15 g was added. The solution was heated with stirring under reflux at 140°C to 150°C for 10 hours while a nitrogen stream was passed through the reaction mixture. The solvent was vacuum distilled off, and 6.1 g of crude product was obtained as residue. (Purity = 91%; Yield = 96%) The crude product was recrystallized from xylene, and a pale yellow powder, 2,2'-methylene-bis-(4-methyl-6-benzotriazolylphenol melting at 285°C was obtained. Example 2 Preparation of 2,2'-methylene-bis-(4-methyl-6-benzotriazolyl-phenol) 6.2 g of the Mannich base obtained in Example 1 and 4-methyl-6-benzotriazolyl-phenol 4.5 g were dissolved in 200 ml of xylene, and sodium methylate (28% methanol solution) 0.2 g was added. The solution was heated with stirring under reflux at 140-150°C for 10 hours with a stream of nitrogen. After distilling of the solvent, and recrystallizing the residue from xylene, the desired product 2,2'-methylene-bis-(4-methyl-6-benzotriazolyl-phenol) was obtained in 95% yield. Example 3 Preparation of 2,2'-methylene-bis-(4-(1,1,3,3-tetramethyl)butyl-6-benzotriazolyl-phenol) 2-Diethylaminomethyl-4-(1,1,3,3-tetramethyl)butyl-6-benzotriazolyl-phenol Mannich base was prepared using 4-(1,1,3,3-tetramethyl)butyl-6-benzotriazolyl-phenol by the same procedure as in Example 1. This Mannich base 37 g and 4-(1,1,3,3-tetramethyl) butyl-6-benzotriazolyl-phenol 25 g were dissolved in 60 ml of xylene, and sodium methylate (28% methanol solution) 3.1 g was added. The solution was heated with stirring under reflux at 140-150°C for 10 hours with a stream of nitrogen. After distilling of the solvent, and recrystallizing the residue from xylene, 55.2 g of the crude product was obtained. (Purity = 93%; Yield = 93%) The crude product was recrystallized from n-heptane, and a white powder, 2,2'-methylene-bis-4-(1,1,3,3-tetramethyl) butyl-6-benzotriazolyl-phenol, melting at 200°C was obtained. Example 4 Preparation of 2,2'-methylene-bis-(4-cumyl-6-benzotriazolyl-phenol) 2-Diethylaminomethyl-4-cumyl-6-benzotriazolyl-phenol Mannich base was prepared using 4-cumyl-6-benzotriazolyl-phenol by the same procedure as in Example 1. This Mannich base 10.0 g and 4-cumyl-6-benzotriazolyl-phenol 6.6 g were dissolved in 60 ml of xylene, and sodium methylate (28% methanol solution) 3.1 g was added. A white crystalline product, 2,2'-methylene-bis-(4-cumyl-6-benzotriazolyl-phenol) melting at 190°C was obtained. (Yield = 93%). Example 5 Preparation of 2,2'-methylene-bis-(4-methyl-6-benzotriazolyl-phenol ) 31.0 g of the Mannich base obtained in Example 1 and methyl iodide 30 g were dissolved in 100 g of ethanol, and heated with stirring at reflux temperature (60°C to 75°C) for 24 hours. The solvent was distilled off, and the pale yellow crystalline product (methyl-diethyl-2-hydroxy-3-benzotriazolyl-5-methylbenzylammonium iodide) was obtained by recrystallization from ethanol. This product 9.0 g and sodium methylate (28% methanol solution) 4.0 g were dissolved in 40 g of butoxyethoxyethanol, and heated with stirring at reflux temperature (160°C to 170°C) for 10 hours while a nitrogen stream was passed through the reaction mixture. The solvent was vacuum distilled off, and 6.1 g of crude product was obtained as residue. (Purity = 91%; Yield = 96%) The crude product was recrystallized from xylene and the desired product, 2,2'-methylene-bis-(4-methyl-6-benzotriazolylphenol) was obtained in 95% yield. The amount of alkylidenebis (benzotriazolyl phenol) is not critical. An amount within the range from about 0.001 to about 5, preferably from about 0.01 to about 3, parts by weight per 100 parts by weight of polyacetal resin is effective. Larger amounts can be used, but are usually unnecessary. The polyacetal resins of this invention are polymers of formaldehyde (monomer), or of a cyclic oligomer of formaldehyde, such as the trimer (trioxane) or the tetramer (tetraoxane), and include oxymethylene homopolymer of the general formula where n is the number of such units in the polymer, and copolymers of formaldehyde with cyclic ethers such as ethylene oxide or glycols, which include [-OCH₂-] units in the copolymer. The copolymers include less than 40 mole %, preferably less than 10 mole %, of oxyalkylene units having two or more carbon atoms in the polymer chain. The resistance of the polyacetal resins to deterioration when heated can be enhanced by known methods,for example, by having terminal hydroxy groups esterified with carboxylic anhydrides. The light stabilizers of this invention are used in combination with polycyclic phenolic antioxidants. These phenolic antioxidants can contain up to about three hundred carbon atoms. Specifically, the polycyclic phenol employed in the compositions of the invention is one having at least two aromatic nuclei linked by a polyvalent linking radical, as defined by the formula: wherein Y is a polyvalent linking group selected from oxygen; carbonyl; sulfur; sulfinyl; sulfonyl; aromatic, aliphatic and cycloaliphatic hydrocarbon groups; and oxyhydrocarbon; thiohydrocarbon and heterocyclic groups. The linking group can have from one up to twenty carbon atoms. Ar is a phenolic nucleus which can be a phenyl or a polycarbocyclic group having condensed or separate phenyl rings; each Ar group contains at least one free phenolic hydroxyl group up to a total of five. The Ar rings can also include additional rings connected by additional linking nuclei of the type Y, for example, Ar-Y-Ar-Y-Ar. m₁ and m₂ are numbers from one to five, and n₁ and n₂ are numbers of one or greater, and preferably from one to four. The aromatic nucleus Ar can, in addition to phenolic hydroxyl groups, include one or more inert substituents. Examples of such inert substituents include hydrogen, halogen atoms, e.g., chlorine, bromine and fluorine; organic radicals containing from one to about thirty carbon atoms, such as alkyl, aryl, alkaryl, aralklyl, cycloalkenyl, cycloalkyl, alkoxy, aryloxy and acyloxy where R¹ is aryl, alkyl or cycloalkyl, or thiohydrocarbon groups having from one to about thirty carbon atoms, and carboxyl groups. Usually, however, each aromatic nucleus will not have more than about eighteen carbon atoms in any hydrocarbon substituent group. The Ar group can have from one to four substituent groups per nucleus. Typical aromatic nuclei include phenyl, naphthyl, phenanthryl, triphenylenyl,anthracenyl, pyrenyl, chrysenyl, and fluoroenyl groups. When Ar is a benzene nucleus, the polyhydric polycyclic phenol has the structure: wherein R₁, R₂ and R₃ are inert substituent groups as described in the previous paragraph; m₁ and m₃ are integers from one to a maximum of five; m₂ is an integer from one to a maximum of four; x₁ and x₃ are zero or integers up to four, and x₂ is zero or an integer up to three; y₁ is zero or an integer up to about six and y₂ is an integer from one to five, preferably one or two. Preferably, the hydroxyl groups are located ortho and/or para to Y. Exemplary Y groups are alkylene, alkylidene, and alkenylene;arylene, alkyl arylene, arylalkylene; cycloalkylene, cycloalkylidene; and oxa- and thia-substituted such groups; tetrahydrofuranes, esters and triazino groups. The Y groups are usually bi, tri, or tetravalent, connecting two, three or four Ar groups. However, higher valency Y groups connecting more than four Ar groups, can also be used. According to their constitution, the Y groups can be assigned to subgenera as follows: 1) Y groups where at least one carbon in a chain or cyclic arrangement connect the aromatic groups, such as: 2) Y groups where only atoms other than carbon link the aromatic rings, such as -O-, -S-, and -(S) x - where x is a number from one to ten; 3) Y groups made up of more than a single atom including both carbon and other atoms linking the aromatic nuclei, such as: Although the relation of effectiveness to chemical structure is insufficiently understood, many of the most effective phenols have Y groups of subgenus 1), and accordingly this is preferred. Some of these phenols can be prepared by the alkylation of phenols or alkyl phenols with polyunsaturated hydrocarbons such as dicyclopentadiene or butadiene. Exemplary polyhydric polycyclic phenols are methylene bis-(2,6-di-tertiary-butyl-phenol), 2,2-bis-(4-hydroxyphenyl)-propane, methylene-bis-(p-cresol), 4,4'-benzylidene bis (2-tertiary-butyl-5-methyl-phenol), 4,4'-cyclo-hexylidene bis-(2-tertiary-butylphenol), 2,2'-methylene-bis-(4-methyl-6-(1'-methyl-cyclohexyl)-phenol), 2,6-bis-(2'-hydroxy-3'-tertiary-butyl-5'-methylbenzyl)-4-methylphenol, 4,4'-bis-(2-tertiary-butyl-5-methyl-phenol), 2,2'-bis-(4-hydroxy-phenyl) butane, ethylene bis-(p-cresol), 4,4'-oxobis-phenol, 4,4'-oxobis-(3-methyl-5-isopropyl-phenol), 4,4'-oxobis-(3-methyl-phenol), 2,2'-oxobis-(4-dodecyl-phenol), 2,2'-oxobis-(4-methyl-5-tertiary-butyl-phenol), 4,4'-thio-bis-phenol; 4,4'-thio-bis-(3-methyl-6-tertiary-butyl-phenol), 2,2'-thio-bis-(4-methyl-6-tertiary-butyl-phenol), 4,4'-n-butylidene-(2-t-butyl-5-methyl-phenol), 2,2'-methylene-bis-(4-methyl-6-(1'-methyl-cyclohexyl)-phenol), 4,4'-cyclohexylene bis-(2-tertiary-butyl-phenol), 2,6-bis-(2'-hydroxy-3'-t-butyl-5'-methyl-benzyl)-4-methyl-phenol, 4,4'-oxobis (naphthalene-1,5-diol), 1,3'-bis-(naphthalene-2,5-diol) propane, and 2,2'-butylene-bis-(naphthalene-2,7-diol), (3-methyl-5-tert-butyl-4-hydroxyphenyl)-4'-hydroxy-phenyl) propane, 2,2'-methylene-bis-(4-methyl-5-isopropylphenol), 2,2'-methylene-bis-(4-methyl-5-isopropylphenol), 2,2'-methylene-bis-(5-tert-butyl-4-chlorophenol), (3,5-di-tert-butyl-4-hydroxyphenyl)-(4'-hydroxyphenyl) ethane, (2-hydroxy-phenyl)-(3',5'-di-tert-butyl-4',4-hydroxyphenyl) ethane, 2,2'-methylene-bis-(4-octylphenol), 4,4'-propylene-bis-(2-tert-butyl-phenol), 2,2'-isobutylene-bis-(4-nonylphenol), 2,4-bis-(4-hydroxy-3-t-buty-phenoxy)-6-(n-octylthio)-1,3,5-triazine, 2,4,6-tris-(4-hydroxy-3-t-butyl-phenoxy)-1,3,5-triazine, 2,2'-bis-(3-t-butyl-4-hydroxyphenyl) thiazolo-(5,4-d) thiazole, 2,2'-bis-(3-methyl-5-t-butyl-4-hydroxyphenyl) thiazolo-(5,4-d)-thiazole, 4,4'-bis-(4-hydroxyphenyl) pentanoic acid octadecyl ester, cyclopentylene-4,4'-bis-phenol, 2-ethylbutylene-4,4'-bisphenol, 4,4'-cyclooctylene-bis-(2-cyclohexylphenol), β,β-thiodiethanol-bis-(3-tert-butyl-4-hydroxyphenoxy acetate), 1,4-butanediol-bis-(3-tert-butyl-4-hydroxyphenoxy acetate), pentaerythritol tetra-(4-hydroxyphenol propionate), 2,4,4'-tri-hydroxy benzophenone, bis-(2-tert-butyl-3-hydroxy-5-methylphenyl) sulfide, his-(2-tert-butyl-4-hydroxy-5-methylphenyl) sulfide, bis-(2-tert-butyl-4-hydroxy-5-methylphenyl )sulfoxide, bis-(3-ethyl-5-tert-butyl-4-hydroxybenzyl) sulfide, bis-(2-hydroxy-4-methyl-6-tert-butyl-phenyl) sulfide, 4,4'-bis-(4-hydroxyphenol) pentanoic acid octadecyl thiopropionate ester, 1,1,3-tris-(2'-methyl-4-hydroxy-5'-tert-butylphenyl) butane, 1,1,3-tris-(1-methyl-3-hydroxy-4-tert-butylphenyl) butane, 1,8-bis-(2-hydroxy-5-methylbenzoyl-n-octane, 2,2'-ethylene-bis-[4'-(3-tert-butyl-4-hydroxyphenyl)-thiazole], 1-methyl-3-(3-methyl-5-tert-butyl-4-hydroxybenzyl)-naphthalene, 2,2'-(2-butene)-bis-(4-methoxy-6-tert-butylphenol)-bis-[3,3-bis-(4-hydroxy-3-t-butylphenyl)butyric acid] glycol ester, 4,4'-butylidene-bis-(6-t-butyl-m-cresol), 1,1,3-tris-(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-tris-(3,5-di-t-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, tetrakis [methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] methane, 1,3,5-tris-(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris-(3,5-di-t-butyl-4-hydroxyphenyl) propionyl-oxyethyl isocyanurate, 2-octylthio-4,6,-di-(4-hydroxy-3,5-di-t-butyl) phenoxy-1,3,5-triazine, 4,4'-thiobis-(6-t-butyl-m-cresol) and pentaerythritol hydroxyphenyl propionate. Additional examples of polycyclic antioxidants include thiodiethylenebis(3,5-di-t-butyl-4-hydroxyphenyl-propionate, hexamethylene-bis(3,5-di-t-butyl-4-hydroxyphenyl-propionate, 2-octylthio-4,6-bis(3,5-di-t-butyl-4-hydroxyphenoxy)-s-triazine, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), bis(3,3-bis(4-hydroxy-3-t-butylphenyl) butyric acid) glycol ester, 2,2'-ethylidenebis(4,6-di-t-butylphenol), 2,2'-ethylidenebis(4-sec-butyl-6-t-butylphenol), 3,6-dioxaoctylenebis(3-methyl-5-t-butyl-4-hydroxyphenylpropionate), bis(2-t-butyl-4-methyl-6-(2-hydroxy-3-t-butyl-5-methylbenzyl) phenyl) terephthalate, 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-t-butylbenzyl) isocyanurate, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, 1,3,5-tris((3,5-di-t-butyl-4-hydroxyphenyl) propionyloxyethyl) isocyanurate, tetrakis (methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate) methane. A particularly desirable class of polyhydric polycyclic phenols are the dicyclopentadiene polyphenols, which are of the type: in which R, and R₂ are lower alkyl, and can be the same or different, and n is the number of the groups enclosed by the brackets, and is usually from 1 to about 5. These are described in US-A-3,567,683. A commercially available member of this class is Wingstay® L, exemplified by dicyclopentadiene tri-(2-tert-butyl-4-methyl-phenol) of the formula: The polyhydric polycyclic phenols used in the invention can also be condensation products of phenols or alkylphenols with hydrocarbons having a bicyclic ring structure and a double bond or two or more double bonds, such as α-pinene, β-pinene, dipentene, limonene, vinylcyclohexene, dicyclopentadiene, allo-ocimene, isoprene and butadiene. These condensation products are usually obtained under acidic conditions in the form of more or less complex mixtures of monomeric and polymeric compounds. However, it is usually not necessary to isolate the individual constituents. The entire reaction product, merely freed from the acidic condensation catalyst and unchanged starting material, can be used with excellent results. While the exact structure of these phenolic condensation products is uncertain, the Y groups linking the phenolic nuclei all fall into the preferred subgenus 1. For method of preparation, see e.g., US-A-3,124,555 and 3,242,135, and GB-A-961,504. In addition, the stabilizer compositions of the invention can include other stabilizers conventionally used as heat and/or light stabilizers for synthetic resins, including polyvalent metal salts of organic acids, organic triphosphites and acid phosphites. When the stabilizer composition is used in conjunction with a polyvalent metal salt of an organic acid, the organic acid will ordinarily have from about six to about twenty-four carbon atoms. The polyvalent metal can be any metal of Group II of the Periodic Table, such as zinc, calcium, cadmium, barium, magnesium and strontium. The alkali metal salts and heavy metal salts such as lead salts are unsatisfactory. The acid can be any organic non-nitrogenous monocarboxyiic acid having from six to twenty-four carbon atoms. The aliphatic, aromatic, alicyclic and oxygen-containing heterocyclic organic acids are operable as a class. By the term "aliphatic acid" is meant any open chain carboxylic acid, substituted, if desired, with nonreactive groups, such as halogen, sulfur and hydroxyl. By the term "alicyclic" it will be understood that there is intended any cyclic acid in which the ring is nonaromatic and composed solely of carbon atoms, and such acids may if desired have inert, nonreactive substituents such as halogen, hydroxyl, alkyl radicals, alkenyl radicals and other carbocyclic ring structures condensed therewith. The oxygen-containing heterocyclic compounds can be aromatic or nonaromatic and can include oxygen and carbon in the ring structure, such as alkyl-substituted furoic acid. The aromatic acids likewise can have nonreactive ring substituents such as halogen, alkyl and alkenyl groups, and other saturated or aromatic rings condensed therewith. As exemplary of the acids which can be used in the form of their metal salts there can be mentioned the following: hexoic acid, 2-ethylhexoic acid, n-octoic acid, isooctoic acid, capric acid, undecylic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, oleic acid, ricinoleic acid, behenic acid, chlorocaproic acid, hydroxy capric acid, benzoic acid, phenylacetic acid, butyl benzoic acid, ethyl benzoic acid, propyl benzoic acid, hexyl benzoic acid, salicylic acid, naphthoic acid, 1-naphthalene acetic acid, orthobenzoyl benzoic acid, naphthenic acids derived from petroleum, abietic acid, dihydroabietic acid, hexahydrobenzoic acid, and methyl furoic acid. The water-insoluble salts are preferred, because they are not leached out when the plastic is in contact with water. Where these sails are not known, they are made by the usual types of reactions, such as by mixing the acid, or anhydride with the corresponding oxide or hydroxide of the metal in a liquid solvent, and heating, if necessary, until salt formation is complete. A variety of organic triphosphites and acid phosphites can be employed, of which the following are exemplary. The organic triphosphite can be any organic phosphite having three or more organic radicals attached to phosphorus through oxygen. The acid phosphite can be any organic phosphite having one or two organic radicals attached to phosphorus through oxygen. These radicals can be monovalent radicals, in the case of the triphosphites, diphosphites and monophosphites. The organic triphosphites in which the radicals are monovalent radicals can be defined by the formula: in which R₁, R₂ and R₃ are selected from alkyl, alkenyl, aryl, alkaryl, aralkyl, and cycloalkyl groups having from one to about thirty carbon atoms. The acid phosphites are defined by the same formula, but one or two of R₁, R₂ and R₃ is hydrogen or a cation of a metal or ammonium. Also included are the organic triphosphites having a bivalent organic radical forming a heterocyclic ring with the phosphorus of the type: in which R₄ is a bivalent organic radical selected from alkylene, arylene, aralkylene, alkarylene and cycloalkylene radicals having from two to about thirty carbon atoms, and R₅ is a monovalent organic radical as defined above in the case of R₁, R₂ and R₃; R₅ is hydrogen or a cation, in the case of the acid phosphites. Also useful organic triphosphites are mixed heterocyclic-open chain phosphites of the type: More complex triphosphites are formed from trivalent organic radicals, of the type: in which R₆ is a trivalent organic radical of any of the types of R₁ to R₅, inclusive, as defined above. A particularly useful class of complex triphosphites are the tetraoxadiphosphaspiro undecanes of the formula: where R, and R₂ are selected from aryl, alkyl, aryloxyethyl, alkyloxyethyl, aryloxyethoxyethyl, alkyloxyethoxyethyl and alkyloxypolyethoxyethyl having from about 1 to about 30 carbon atoms. In the case of the acid phosphites, one or both of R₁ and R₂ is also hydrogen or a cation. An especially preferred class of organic triphosphites and acid phosphites have a bicyclic aromatic group attached to phosphorus through oxygen, with no or one or more phenolic hydroxyl groups on either or both of the aromatic rings. These phosphites are characterized by the formula; or in which Ar is a mono or bicyclic aromatic nucleus and m is zero or an integer of from 1 to about 5. is one or a plurality of organic radicals as defined above for R, to R₆, taken singly or together in sufficient number to satisfy the valences of the two phosphite oxygen atoms. One or both of said radicals is also hydrogen, in the case of the acid phosphites, and can include additional bicyclic aromatic groups of the type (HO) m -Ar. The cation in the case of acid phosphites can be a metal, such as an alkali metal, for instance, sodium, potassium or lithium; an alkaline earth metal, for instance, barium, calcium, or a nontoxic polyvalent metal, such as magnesium, tin and zinc. Usually, the triphosphites and acid phosphites will not have more than about sixty carbon atoms. Exemplary triphosphites are monophenyl di-2-ethylhexyl phosphite, diphenyl mono-2-ethylhexyl phosphite, di-isooctyl monotolyl phosphite, tri-2-ethylhexyl phosphite, phenyl dicyclohexyl phosphite, phenyl diethyl phosphite, triphenyl phosphite, tricresyl phosphite, tri(dimethylphenyl) phosphite, trioctadecyl phosphite, triisooctyl phosphite, tridodecyl phosphite, isooctyl diphenyl phosphite, diisooctyl phenyl phosphite, tri(t-octylphenyl) phosphite, tri-(t-nonylphenyl) phosphite, benzyl methyl isopropyl phosphite, butyl dicresyl phosphite, isooctyl di(octylphenyl) phosphite, di(2-ethylhexyl)(isooctylphenyl) phosphite, tri (2-cyclohexylphenyl) phosphite), tri-α-naphthyl phosphite, tri (phenylphenyl) phosphite, tri(2-phenylethyl) phosphite, ethylene phenyl phosphite, ethylene t-butyl phosphite, ethylene isohexyl phosphite, ethylene isooctyl phosphite, ethylene cyclohexyl phosphite, 2-pheno-1,3,2-dioxaphosphorinane, 2-butoxy-1,3,2-dioxaphosphorinane, 2-octoxy-5,5-dimethyl-dioxaphosphorinane, and 2-cyclohexyloxy-5,5-diethyl dioxaphosphorinane. Exemplary pentaerythritol triphosphites are 3,9-diphenoxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane (diphenyl-pentaerythritol diphosphite), 3,9-di(decyloxy)-2,4,8, 10-tetraoxa-3,9-diosphaspiro-(5,5)-undecane, 3,9-di (isodecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3-pheno-9-isodecyloxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di-(methoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di(lauryloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di-p-tolyloxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane; 3,9-di(methoxyethyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3-methoxyethyloxy-9-isodecyloxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di(ethoxyethyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di(butoxyethyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, . 3-methoxyethyloxy-9-butoxy-ethyloxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di(methoxyethoxyethyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di-(butoxyethoxyethyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di(methoxyethoxyethoxyethyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane, 3,9-di(methoxy (polyethoxy)ethyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane,where the (polyethoxy) ethyloxy group has an average molecular weight of 350), 3,9-di(methoxy(polyethoxy) ethyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro-(5,5)-undecane (where the (polyethoxy) ethyloxy group has an average molecular weight of 550). Exemplary of the bis aryl triphosphites are: bis(4,4'-thio-bis(2-tertiary-butyl-5-methyl-phenol)) isooctyl phosphite, mono(4,4'-thio-bis(2-tertiary-butyl-5-methyl-phenol)) di-phenyl phosphite, tri-(4,4'-n-butylidene-bis(2-tertiary-butyl-5-methyl-phenol)) phosphite, (4,4'-benzylidene-bis(2-tertiary-butyl-5-methyl-phenol)) diphenyl phosphite, isooctyl 2,2'-bis(para-hydroxyphenyl) propane phosphite, decyl 4,4'-n-butylidene-bis (2-tertiary-butyl-5-methylphenol) phosphite, tri-4,4'-thio-bis (2-tertiary-butyl-5-methylphenol) phosphite, 2-ethylhelxyl-2,2'-methylene-bis(4-methyl-6,1'-methylcyclohexyl) phenol phosphite, tri(2,2'-bis-(para-hydroxyphenyl) propane) phosphite, tri(4,4'-thio-bis(2-tertiary-butyl-5-methyl-phenol) phosphite, isooctyl-(2,6-bis(2'-hydroxy-3,5-dinonylbenzyl)-4-nonyl phenyl)) phosphite, tetra-tridecyl-4,4'-n-butylidene-bis(2-tertiary-butyl-5-methylphenyl) diphosphite, tetra-isooctyl-4,4'-thio-bis (2-tertiary-butyl-5-methylphenyl) diphosphite, 2,2'-methylene-bis(4-methyl-6,1'-methyl cyclohexyl phenyl) polyphosphite, isooctyl-4,4'-isopropylidene-bis-phenyl polyphosphite, 2-ethylhexyl-2,2'-methylene-bis(4-methyl-6,1'-methyl-cyclohexyl) phenyl triphosphite, tetra-tridecyl-4,4'-oxydiphenyl-diphosphite, tetra-n-dodecyl-4,4'-n-butylidene bis (2-tertiary-butyl-5-methylphenyl) diphosphite, tetra-tridecyl-4,4'-isopropylidene bisphenyl diphosphite, hexa-tridecyl butane-1,1,3-tris(2'-methyl-5'-tertiary-butylphenyl-4') triphosphite. Exemplary acid phosphites are di(phenyl) phosphite, monophenyl phosphite, mono(diphenyl) phosphite, dicresyl phosphite, di-(o-isooctylphenyl) phosphite, di(p-ethylhexylphenyl) phosphite, di(p-t-octylphenyl) phosphite, di(dimethylphenyl) phosphite, di-n-butyl phosphite, di-2-ethylhexyl phosphite, mono-2-ethylhexylphosphite, diisooctyl phosphite, monoisooctyl phosphite, monododecyl phosphite, 2-ethylhexyl phenyl phosphite, 2-ethylhexyl-(n-octylphenyl) phosphite, monocyclohexyl phosphite, dicyclohexyl phosphite, di(2-cyclohexyl phenyl) phosphite, di-α-naphthyl phosphite, diphenyl phenyl phosphite, di(diphenyl) phosphite, di-(2-phenyl ethyl) phosphite, dibenzyl phosphite, monobenzyl phosphite, n-butyl cresyl phosphite and didodecyl phosphite, cresyl phosphite, t-octylphenyl phosphite, ethylene phosphite, butyl cresyl phosphite, isooctyl monotolyl phosphite add phenyl cyclohexyl phosphite. Exemplary of the bis aryl acid phosphites are: bis(4,4'-thio-bis(2-tertiary-butyl-5-methylphenol)) phosphite, (4,4'-thio-bis(2-tertiary-butyl-5-methylphenol)) phenyl-phosphite, bis(4,4'-n-butylidene-bis(2-tertiary-butyl-5-methyl-phenol)) phosphite, mono(4,4'-benzylidene-bis(2-tertiary-butyl-5-methylphenol)) phosphite, mono(2,2'-bis-(parahydroxyphenyl) propane) phosphite, mono(4,4'-butylidene-bis(2-tertiary-butyl-5-methylphenol) phosphite, bis(4,4'-thio-bis(2-tertiary-butyl-5-methylphenol)) phosphite, mono-2-ethylhexyl-mono-2,2-methylene-bis(4-methyl-6,1'-methylcyclohexyl) phenol phosphite, bis (2,2'-bis(para-hydroxyphenyl)propane)phosphite, monoisooctyl-mono(4,4'-tihio-bis(2-tertiary-butyl-5-methylphenol)) phosphite, isooctyl-(2,6-bis(2'-hydroxy-3,5-dinonylbenzyl)-4-nonylphenyl)) phosphite, tri-tridecyl-4,4'-n-butylidene-bis(2-tertiary-butyl-5-methylphenyl) diphosphite, triisooctyl-4,4'-thio-bis(2-tertiary-butyl-5-methylphenyl) diphosphite, bis(2,2'-methylene-bis(4-methyl-6,1'-methyl cyclohexyl phenyl)) phosphite, isooctyl-4,4'-isopropylidene-bis-phenyl phosphite, monophenyl mono(2,2'-methylene-bis(4-methyl-6,1'-methyl-cyclohexyl)) triphosphite, di-tridecyl-4,4'-oxydiphenyl diphosphite, di-n-dodecyl-4,4'-n-butylidene-bis(2-tertiary-butyl-5-methylphenyl) diphosphite, di-tridecyl-4,4'-isopropylidene bisphenyl diphosphite, tetra-tridecyl butane-1,1,3-tris(2'-methyl-5-tertiary-butylphenyl-4)-triphosite. The thiodipropionic acid ester has the following formula: R₁OOCCH₂CH₂-S-CH₂CH₂COOY in which R₁ is an organic radical selected from hydrocarbon radicals such as alkyl, alkenyl, aryl, cycloalkyl and mixed alkyl aryl and mixed alkyl cycloalkyl radicals; hydroxyalkyl and hydroxyalkoxyalkylene radicals; and esters thereof with aliphatic carboxylic acids; and Y is selected from (a) hydrogen, (b) a second R radical R₂, which can be the same as or different from the R₁ radical, (c) a polymeric chain of thiodipropionic acid ester units: -XO[OCCH₂CH₂SCH₂CH₂COOXO] n OCCH₂CH₂-S-CH₂CH₂COOZ where Z is hydrogen, R₂ or M, n is the number of thiodipropionic acid ester units in the chain, and X is a bivalent hydrocarbon group of the type of R₁,that is, alkylene, alkenylene, cycloalkylene, mixed alkylene-arylene and mixed alkylenecycloalkylene radicals; hydroxyalkylene and hydroxyalkyloxyalkylene radicals; and esters thereof with aliphatic carboxylic acids; the value of n can range upwards from 0, but there is no upper limit on n except as is governed by the ratio of carbon atoms to sulfur atoms as stated below; and (d) a polyvalent metal M of Group II of the periodic table such as zinc, calcium, cadmium, barium, magnesium and strontium. The molecular weights of the R and Y radicals are taken such that with the remainder of the molecule the thiodipropionic ester has a total of from about ten to about sixty carbon atoms per sulfur atom. Accordingly, the various thiodipropionic acid ester species coming within the above-designated categories within the general formula can be defined as follows: (a) R₁OOCCH₂CH₂SCH₂CH₂COOH (b) R₁ OOCCH₂CH₂SCH₂CH₂COOR₂ (d) R₁OOCCH₂CH₂SCH₂CH₂COOM In the above formulae R₁ and R₂, M, X and Z are the same as before and the value of n₁ can range upwards from 1, but there is no upper limit on n₁ except as is imposed by the ratio of carbon atoms, as stated below. In the polymer (c), as in the other forms of thiodipropionic acid esters, the total number of carbon atoms per sulfur atom is within the range from about ten to about sixty. The R radical of these esters is important in furnishing compatibility with the polymer. The Y radical is desirably a different radical, R₂ or M or a polymer, where R is rather low in molecular weight, so as to compensate for this in obtaining the optimum compatibility and nonvolatility. Where Y is a metal, the thiodipropionic acid ester furnishes the beneficial properties of the polyvalent metal salt which is described above. The aryl, alkyl, alkenyl, and cycloalkyl groups may, if desired, contain inert, nonreactive substituents such as halogen and other carbocyclic and heterocyclic ring structures condensed therewith Typical R radicals are, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, amyl, isoamyl, n-octyl, isooctyl, 2-ethyl hexyl, t-octyl, decyl, dodecyl, octadeyl, allyl, hexenyl, linoleyl, ricinoleyl, oleyl, phenyl, xylyl, tolyl, ethylphenyl, naphthyl, cyclohexyl, benzyl, cyclopentyl, methylcyclohexyl, ethylcyclohexyl, and naphthenyl, hydroxyethyl, hydroxypropyl, glyceryl, sorbityl, pentaerythrityl, and polyoxyalkylene radicals such as those derived from diethylene glycol, triethylene glycol, polyoxypropylene glycol, polyoxyethylene glycol, and polyoxypropyleneoxyethylene glycol, and esters thereof with any of the organic acids named below in the discussion of the polyvalent metal salts, including in addition those organic acids having from two to five carbon atoms, such as acetic, propionic, butyric and valeric acids. Typical X radicals are alkylene radicals such as ethylene, tetramethylene, hexamethylene, decamethylene, alkyl-substituted alkylene radicals such as 1,2-propylene, arylene radicals such as phenylene methylenephenylene dimethylene phenylene and alicyclylene such as cyclohexylene and cyclopentylene As exemplary of the thiodipropionic acid esters which can be used, there can be mentioned the following: monolauryl thiodipropionic acid, dilauryl thiodipropionate, butyl stearyl thiodipropionate, 2-ethylhexyl lauryl thiodipropionate, di-2-ethylhexyl-thiodipropionate, diisodecyl thiodipropionate, isodecyl phenyl thiodipropionate, benzyl lauryl thiodipropionate, benzyl phenyl thiodipropionate, the diester of mixed coconut fatty alcohols and thiodipropionic acid, the diester of mixed tallow fatty alcohols and thiodipropionic acid, the acid ester of mixed cottonseed oil fatty alcohols and thiodipropionic acid, the acid ester of mixed soybean oil fatty alcohols and thiodipropionic acid, cyclohexyl nonyl thiodipropionate, monooleyl thiodipropionic acid, hydroxyethyl lauryl thiodipropionate, monoglyceryl thiodipropionic acid, glyceryl monostearate monothiodipropionate, sorbityl isodecyl thiodipropionate, the polyester of diethylene glycol and thiodipropionic acid, the polyester of triethylene glycol and thiodipropionic acid, the polyester of hexamethylene glycol and thiodipropionic acid, the polyester of pentaerythritol and thiodipropionic acid, the polyester of octamethylene glycol and thiodipropionic acid, the polyester of p-dibenzyl alcohol and thiodipropionic acid, ethylbenzyl lauryl thiodipropionate, strontium stearyl thiodipropionate, magnesium oleyl thiodipropionate, calcium dodecylbenzyl thiodipropionate, and mono(dodecylbenzyl) thiodipropionic acid. These esters are for the most part known compounds, but where they are not available, they are readily prepared by esterification of thiodipropionic acid and the corresponding alcohol. Also useful are: (1) Thioalkanoic acid amides of JP-A-16,286/68 having the formula: wherein R is alkyl of one to eight carbon atoms, R₁ is alkyl of six to twenty-four carbon atoms, and R₂ is alkylene of one to six carbon atoms. (2) Thioalkanoic acid amides of 1,3,5-triazines of JP-A-20,366/68 having the formula: wherein R is alkyl of eight to eighteen carbon atoms. (3) Bis-thioalkanoic acid amides of JP-A-23, 765/68 having the formula: wherein R is alkyl of more than six carbon atoms, aryl or aralkyl. (4) Bis-thioalkylanoic acid amides of JP-A- 26,184/69 having the formula: wherein R is alkyl of twelve to eighteen carbon atoms, and R₁ is alkylene of one to ten carbon atoms, cycloalkylene, or arylene. (5) Bis-alkylene thioalkanoic acid amides of JP-A-31,464/69 having the formula: wherein R is alkyl of more than six carbon atoms, aryl, or aralkyl. (6) Thioalkanoic acid amide derivatives of JP-A-106,484/74 having the formula: wherein R is hydrocarbyl of one to twenty carbon atoms. (7) Alkylene bis-thioalkanoic acid amides of US-A-4,279,805 having the general formula: wherein: R₁ is alkyl having from one to about fifty carbon atoms; R₂ is alkylene having from one to about three carbon atoms; and R₃ is alkylene having from about two to about twelve carbon atoms. β-Alkythiopropionic acid esters having the general formula: R-S-C₂H₄COOR(R') n wherein: R is alkyl of four to twenty carbon atoms; n is a number from 1 to 6; and R' is the residue of an alcohol having from one to six hydroxyl groups. Pentaerythritol tetra dodecyl thio propionate is an example of this group. Other conventional light stabilizers can be employed, such as hydroxybenzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxy benzophenone, 2,4-dihydroxybenzophenone, benzotriazoles, such as 2(2-hydroxy-5 methylphenyl) benzotriazoles, 2(2-hydroxy-3-t-butyl-5-methylpenyl)-5-chlorobenzotriazole, 2(2-hydroxy-3-5-di-t-butylphenyl) 5-chlorobenzotriazole, 2(2-hydroxy-3,5-di-t-amylphenyl) benzotriazole, benzoates such as phenylsalicylate, 2,4-di-t-butylphenyl -3,5-di-t-butyl-4-hydroxy phenylbenzoate, nickel compounds such as nickel-2,2'-thiobis(4-t-octyl-phenolate), nickel-monoethyl(3,5-di-t-butyl-4-hydroxybenzyl)phosphonate, substituted acrylonitriles such as methyl-α-cyano-β-methyl-β-(p-methoxy phenyl)acrylate and oxalic anilides such as N-2-ethyl phenyl-N'-2-ethoxy-5-t-butyl phenyl oxalic diamide, N-2-ethyl phenyl-N'-2-ethoxy phenyl oxalic diamide. A sufficient amount of the stabilizer composition is used to improve the resistance of the synthetic polymer to deterioration in physical properties then exposed to heat and light, including, for example, discoloration, reduction in melt viscosity and embrittlement. Very small amounts are usually adequate. Amounts within the range from about 0.001 to about 10% total stabilizers including the light stabilizer system of the invention by weight of the polymer are satisfactory. Preferably, from 0.01 to 5% is employed for optimum stabilization. Inasmuch as all components are solids, the stabilizer systems of the invention are readily rendered in solid particulate form, comprising a blend of: (a) a heat stabilizer for the synthetic polymer in an amount of from about 10 to about 35 parts by weight; (b) alkylidene bis(benzotriazolyl phenol) or polymer thereof in an amount of from about 10 to about 35 parts by weight; The heat stabilizer is (c) a phenolic antioxidant as defined above in an amount from about 10 to about 35 parts by weight; and optionally, (d) other heat stabilizers in an amount of from about 10 to about 35 parts by weight. The amount of the phenolic antioxidant employed according to the invention is within the range from 0.001 to 3 parts by weight, preferably from 0.005 to 1 part by weight, per 100 parts by weight of polyacetal resin. In addition, other conventional additives for synthetic polymers, such as plasticizers, lubricants, emulsifiers, anti-static agents, flame-proofing agents, pigments and fillers, can be employed. The stabilizer composition is incorporated in the polymer in suitable mixing equipment, such as a mill or a Banbury mixer. If the polymer has a melt viscosity which is too high for the desired use, the polymer can be worked until its melt viscosity has been reduced to the desired range before addition of the stabilizer. Mixing is continued until the mixture is substantially uniform. The resulting composition is then removed from the mixing equipment and brought to the size and shape desired for marketing or use. The stabilized polymer can be worked into the desired shape, such as by milling, calendering, extruding or injection molding or fiber-forming. In such operations, it will be found to have a considerably improved resistance to reduction in melt viscosity during the heating, as well as a better resistance to discoloration and embrittlement on ageing and heating. The following Examples represent preferred polyacetal resin compositions of the invention. Examples 1 to 5 Polyacetal resin compositions were prepared, using stabilizers of this invention, and having the following formulation: Ingredient Parts by weight Polyoxymethylene homopolymer (Tenac 5010: Asahi Chemical Industries) 100 2,2'-Methylenebis(4-methyl-6-t-butylphenol) 0.2 Stabilizer as shown in Table I 0.3 The compositions were thoroughly blended in a Brabender Plastograph, and then extruded to form pellets. The pellets were then injection-molded at 200°C, 600kg/cm², to form test pieces 1 mm thick. The test pieces exposed to ultraviolet light in a Sunshine Weather-O-Meter. The hours to failure were noted, and are shown inTable I. Example No. Stabilizer Hours to Failure Control 1 2-(2'-Hydroxy-5-methylphenyl) benzotriazole 280 Control 2 2-(2'-Hydroxy-3',5'-di-t-amylphenyl) benzotriazole 420 Control 3 2-(2'-Hydroxy-3',5'-dicumylphenyl) benzotriazole 650 Example 1 2,2'-Methylenebis(4-methyl-6-benzotriazolyl phenol) 900 Example 2 2,2'-Methylenebis (4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolyl phenol) 980 Example 3 2,2'-Methylenebis(4-cumyl-6-benzotriazolyl phenol) 960 Example 4 2,2'-Octylidenebis(4-methyl-(5'-methylbenzotriazolyl) phenol) 820 Example 5 2,2'-Octylidenebis(4-methyl-(5'-chlorobenzotriazolyl) phenol) 840 The improvement when using an alkylidene bis (benzotriazolyl phenol) of the invention is apparent from comparison with the mono (benzotriazolyl phenols) of the controls. Examples 6 to 10 Polyacetal resin compositions were prepared using stabilizers of this invention and having following formulation: Ingredient Parts by weight Trioxane/ethylene oxide copolymer (Duracon M-20: Polyplastic Co.,) 100 3, 6-Dioxaoctylenebis (β-(3,5-di-t-butyl-4-hydroxyphenyl) propionate) 0.3 Stabilizer as shown in Table II 0.2 The compositions were thoroughly blended in a Brabender Plastograph, and then extruded to form pellets. The pellets were then injection-molded at 200°C, 600 kg/cm² to form test pieces 1 mm thick. The test pieces exposed to ultraviolet light in a Sunshine Weather-O-Meter for 150 hours, and elongation before and after irradiation was measured. The results are shown in Table II as % elongation retained. Example No. Stabilizer % Elongation retained Control 1 2-(2'-Hydroxy-5-methylphenyl) benzotriazole 52 Control 2 2-(2'-Hydroxy-3' , 5'-di-t-amylphenyl) benzotriazole 53 Control 3 2-(2'-Hydroxy-3',5'-dicumylphenyl) benzotriazole 55 Example 6 2,2'-Methylenebis(4-methyl-6-benzotriazolyl phenol) 75 Example 7 2, 2'-Methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolyl phenol) 81 Example 8 2,2'-Methylenebis(4-cumyl-6-benzotriazolyl phenol) 79 Example 9 2,2'-octylidenebis(4-methyl-(5'-methylbenzotriazolyl) phenol) 66 Example 10 2,2'-Octylidenebis(4-methyl-(5' chlorobenzotriazolyl) phenol) 65 The improvement when using an alkylidene bis (benzotriazolyl phenol) of the invention is apparent from comparison with the mono (benzotriazolyl phenols) of the controls.

Claims: A polyacetal resin composition having improved resistance to deterioration when exposed to light, comprising a polyacetal resin, an alkylidene bis(benzotriazolyl phenol) having the formula: wherein: R₁ is selected from hydrogen and alkyl having from one to eleven carbon atoms: R₂ is selected from alkyl having from one to twelve carbon atoms; and arylalkyl having from seven to eighteen carbon atoms; and X is selected from hydrogen; halogen; alkyl having from one to twelve carbon atoms; arylalkyl having from seven to eighteen carbon atoms; alkoxy having from one to twelve carbon atoms; phenoxy; arylalkoxy having from seven to eighteen carbon atoms; and phenyl; and a polycyclic phenolic antioxidant in an amount from 0.001 to 3 parts by weight per 100 parts by weight of polyacetal resin, having the formula wherein Y is a polyvalent linking group selected from oxygen; carbonyl; sulfur; sulfinyl; sulfonyl; aromatic, aliphatic and cycloaliphatic hydrocarbon groups, and oxyhydrocarbon, thiohydrocarbon and heterocyclic groups, Ar is a phenolic nucleus which is a phenyl or a polycarbocyclic group having condensed or separate phenyl rings, with or without additional rings connected by additional linking nuclei of the type Y, each Ar group containing from one up to a total of five free phenolic hydroxyl groups, m₁ and m₂ are numbers from one to five, and n₁ and n₂ are numbers of one or greater. A polyacetal resin composition according to claim 1 in which the polyacetal resin is oxymethylene homopolymer, or trioxane-ethylene oxide copolymer. A polyacetal resin composition according to one or both of the claims 1-2 in which R₁ is hydrogen. A polyacetal resin composition according to one or both of the claims 1-2 in which R₁ is alkyl. A polyacetal resin composition according to one or more of the claims 1-4 in which R₂ is alkyl. A polyacetal resin composition according to one or more of the claims 1-4 in which R₂ is arylalkyl. A polyacetal resin composition according to one or more of the claims 1-6 in which X is hydrogen. A polyacetal resin composition according to one or more of the claims 1-6 in which X is halogen. A polyacetal resin composition according to one or more of the claims 1-6 in which X is alkyl.

Inventors: KUBOTA, NAOHIRO, NISHIMURA, ATSUSHI
Applicants: ADEKA ARGUS CHEMICAL CO., LTD.
Application year: 1986
Main classification: C08K5
IPC codes: C08K5, C08L59