POLYUNSATURATED HYDROCARBON POLYMER-COMPATIBLE ANTIOXIDANT COMPOSITIONS

Abstract: A polyunsaturated hydrocarbon-polymer-compatible antioxi­ dant composition that comprises a mixture of a sterically hindered phenolic compound and an aryl amine compound in a molar ratio ranging from about 0.1 to about 10.

Description: This invention relates to antioxidant stabilizing systems for polymers, formed from the ring-opening, metathesis-catalyst polymerization of norbornene-type monomers, that effectively delay degradation by olefin oxidation of the polymer's physical properties. Norbornene-type monomers, which are defined for the purpose of this invention as dicyclopentadiene, tricyclopentadiene and other oligomers of dicyclopentadiene, norbornene, norbornadiene, 1,4,5,8-dimethano-1,4,4a,5,8,8a-hexahydronaphthalene and 1,4,5,8-dimethano-1,4,4a,5,8,8a-hexahydronaphthalene (DMHN), and 1,4,5,8-dimethano-1,4,4a,5,8,8a-octahydronaphthalene (DMON), are known to undergo ring-opening polymerization reactions in the presence of a metathesis catalyst to form, high modulus, high impact-strength polyunsaturated hydrocarbon polymers. U.S. Patent 4,400,340 describes the production of a poly(dicyclopentadiene) (PDCP) polymer from the metathesis catalyst ring-opening polymerization of dicyclopentadiene, and U.S. Patent 4,568,660 describes the metathesis catalyst ring-opening copolymerization of dicyclopentadiene with such norbornene-type polycycloolefins as DMHN and DMON. Such polymers, however, are subject to degradation of physical properties such as tensile elongation, structural integrity, modulus and impact strength by olefin oxidation on exposure to light, heat and/or air over substantial periods of time. Various antioxidant stabilizers have been proposed to delay such oxidation. For example, hindered phenolic and aryl amine compounds have been found useful as antioxidant stabilizing compounds for these polymers. In CA; Vol 82, 1975, Nr. 59425 p the use of a combination of two antioxidants in the composition of synergetic mixtures for the stabilization of cis-1,4-polybutadiene is described. CA; Vol 73; 1970, Nr. 121396 describes synergistic mixtures for chloroprene stabilization wherein the mixture was composed of phenolic antioxidants and primary and secondary amines. JP-A-57-166 237 describes a ring opening polymer composition having improved heat resistance. As heat resistant stabilizer are proposed 1-naphthylamine and a sterically hindered phenolic compound. EP 42589 discloses norbornene polymers stabilized with hindered aromatic alcohols. Hindered phenolic compounds by themselves, however, have limited effectiveness as antioxidant stabilizing compounds in delaying degradation of tensile elongation and impact strength, such properties exhibiting degradation after relatively short aging time. Aryl amine compounds have been found to afford more protection than phenolic compounds against the loss of physical properties by oxidation of olefinic material, but the rate of such degradation is still undesirably high. Moreover, unlike hindered phenolic compounds, some aryl amines, for example, N,N'-diphenyl-phenylenediamine, when used alone, are incompatible with polymers such as PDCP, and tend to "bleed" or otherwise migrate to the surface of such polymeric material. Such bleeding can cause polymer discoloration and staining of painted polymer surfaces by migration through the paint film. There is therefore a need to provide a composition containing a norbornene-type monomer, such as dicyclopentadiene, that is polymerizable by a ring-opening metathesis catalyst and an antioxidant stabilizer for the polymer formed that is compatible with the polymer, delays degradation by olefin oxidation of physical properties of the polymer, and avoids discoloration of either the polymers or any of the paint systems that are likely to be applied on the polymer for aesthetic purposes. According to the invention, a composition polymerizable by a ring-opening metathesis-catalyst, comprising dicyclopentadiene or another norbornene-type monomer and a sterically-hindered phenolic compound as an antioxidant stabilizer, is characterized In that the stabilizer is a synergistic antioxidant mixture that is compatible with polyunsaturated hydrocarbon polymers and comprises: (a) a sterically hindered phenolic compound having one of the following general formulas: in which A represents a mono or polyvalent organic radical selected from a straight-chain or branched C₁ to C₂₀-saturated aliphatic group, a straight-chain or branched C₂ to C₂₀-unsaturated aliphatic group, an aryl group, a C₇ to C₂₀-aralkyl group, or a C₇ to C₂₀-aralkenyl group; and m represents a positive integer from 0-20, and n represents a positive integer from 1-20, and p and q each represent a positive integer from 1-4; or 4-hydroxymethyl-2,6-ditertiarybutyl phenol or thiodiethylene bis(3,5-ditertiarybutyl-4-hydroxy)-hydrocinnamate (b) at least one aryl amine compound having one of the following general formulas: in which R₁ and R₂ are the same or different aryl groups in which R₃ and R₄ are the same or different and can be hydrogen atoms, or straight-chain or branched C₁ to C₂₀-alkyl groups, straight-chain or branched C₂ to C₂₀-alkylene groups, aryl groups, C₇ to C₂₀-aralkyl groups or a C₇ to C₂₀-aralkenyl groups, or radicals having one of the following formulas: in which n represents a positive integer from 1-20, the sterically hindered phenolic compound and aryl amine compound being present in a molar ratio ranging from about 0.1 to about 10. The synergistic antioxidant mixture in the ring-opening metathesis catalyst polymerizable composition according to the invention is compatible with the polyunsaturated polymer produced and significantly and unexpectedly delays the onset of loss of the polymeric product's physical properties by oxidation as compared to the relatively poor oxidation protection offered by currently available antioxidants. Further, it does not cause polymer discoloration or discoloration of any paint applied to the polymer. Examples of sterically hindered phenolic compounds suitable for use in the present invention include: 2,6-ditertiarybutyl-4-methylphenol, 2,6-ditertiarybutyl-4-ethyl phenol, 2,6-ditertiarybutyl-4-n-butyl phenol, 4-hydroxymethyl-2,6-ditertiarybutyl phenol, and such commercially available compounds as thiodiethylene bis(3,5-ditertiarybutyl-4-hydroxyl)hydrocinnamate, octadecyl 3,5-ditertiarybutyl-4-hydroxyhydrocinnamate, 1,6-hexamethylene bis(3,5-ditertiarybutyl-4-hydroxyhydrocinnamate), and tetrakis(methylene(3,5-ditertiary-butyl-4-hydroxyhydrocinnamate)methane, all available as Irganox 1035, 1076, 259 and 1010, respectively, from Ciba-Geigy Corporation. Other examples of sterically hindered phenolics useful herein include 1,3,5-trimethyl-2,4,6-tris(3,5-ditertiarybutyl-4-hydroxybenzyl)benzene and 4,4′-methylene-bis(2,6-ditertiarybutylphenol), available as Ethyl 330 and 702, respectively, from Ethyl Corporation. Suitable aryl amine compounds that can be used include, for example, various commercially available compounds such as diphenylamine (DPA), N,N′-diphenyl-para-phenylene diamine, N,N′-dibeta-naphthyl-para-phenylene diamine, dioctylated diphenylamine and octylated diphenylamine, all available as Agerite DPPD, White, Stalite S and Stalite, respectively, from R. T. Vanderbilt Company, Inc.; p-orientated styrenated diphenylamine and dimethyl diaryl-para-phenylenediamine, both available as Wingstay 29 and 200, respectively, from Goodyear Tire & Rubber Co.; Preferably, the antioxidant mixture comprises dicyclopentadiene or a mixture of dicyclopentadiene with one or more such norbornene-type monomers. While the ring-opening metathesis-catalyst polymerization of the resulting monomer mixture can be carried out by a variety of procedures and catalyst systems known in the art to produce a polymer, copolymer or terpolymer, the preferred method is the reaction injection molding (RIM) method (which is well-known, for example from U.S. Patent 4,400,340). In that method at least two streams comprising a two-part metathesis-catalyst system are mixed together, the combined streams then being injected into a mold where they quickly set up into a solid polymerized mass. In the two-part metathesis-catalyst system, one part (A), contains a mixture of polymerizable monomer and at least one soluble tungsten-containing catalyst, such as tungsten halide or tungsten oxyhalide, preferably WCl₆ or WOCl₄. The other part (B), which also contains polymerizable monomer, contains at least one organoaluminum catalyst activator selected from the group of compounds consisting of trialkylaluminum compounds, dialkylaluminum halides, alkylaluminum dihalides and alkylaluminum sesquihalides wherein the alkyl group contains from 1 to 12 carbon atoms. In a preferred catalyst activator, the alkyl group is ethyl with diethyl aluminum chloride being the most preferred. The sterically hindered phenolic-aryl amine antioxidant composition can be incorporated into the polymerizable monomer mixture of either part of the above described catalyst system; however, it is preferred to incorporate the mixture into part (A). In an alternative embodiment, a three stream RIM may be employed wherein the sterically hindered phenolic-aryl amine antioxidant mixture is incorporated into a third stream containing only polymerizable monomer, part (C), that is separate from the streams of parts (A) and (B) above containing catalyst and catalyst activator, respectively. The relative proportion of sterically hindered phenolic-aryl amine antioxidant composition in accordance with this invention, can vary about 0.25 to about 4 parts by weight, preferably from about 0.25 to about 2 parts per 100 parts by weight of polymerizable monomer. In accordance with this invention, the tungsten compounds are employed at a level of from about 0.3 to about 1.5 millimoles, preferably from about 0.4 to about 0.6 millimoles per mole of polymerizable monomer mixture of part (A) of the above-mentioned catalyst system. The organoaluminum catalyst activator compounds are useful in this invention at levels ranging from about 1.0 to about 3.5 millimoles, preferably from about 1.2 to about 1.8 millimoles per mole of polymerizable monomer mixture of part (B) of the aforementioned catalyst system. The tungsten catalyst compounds are conventionally dissolved in a solvent prior to incorporation into the monomer mixture of part (A) of the catalyst system. Preferably, the tungsten compound is first suspended in a suitable non-reactive solvent, for example, an aromatic solvent such as benzene, toluene, xylene, chlorobenzene, dichlorobenzene or trichlorobenzene, then solubilized by the addition of an alcoholic or phenolic compound, preferably, phenol, alkyl phenols, or halogenated phenols, with tert-butyl phenol, tert-octyl phenol and nonyl phenol being the most preferred. The preferred molar ratio of tungsten compound-phenolic compound can range from about 1:1 to about 1:3. The organoaluminum activator compounds are also preferably dissolved in a solvent such as those described above prior to use in this invention. Usually, as described in U.S. Patent No. 4,400,340, a stabilization agent is added to the monomer mixture of part (A) of the catalyst system to prevent premature monomer polymerization and to prolong the storage life of this component. Such compounds useful in this invention in amounts ranging from about 1 to about 5 moles per mole of tungsten compound preferably include chelating, and/or complexing agents, for example, acetylacetones, alkylacetoacetates wherein the alkyl group contains from 1 to 10 carbon atoms, and Lewis bases, for example, benzonitrile and tetrahydrofuran. Further, it is well-known that the metathesis-catalyst polymerization of polymerizable monomer by the (RIM) method must be delayed to prevent the polymerizable mixture from setting up prematurely in the mixing head. This can be accomplished by the addition of a reaction rate moderator to part (B) of the catalyst system. Examples of compounds useful as reaction rate moderators for the alkylaluminum compounds contained in part (B) in accordance with this invention include ethers, esters, ketones, nitriles and polar cycloolefins, with ethyl benzonate, isopropyl ether, butyl ether and bis(alpha-methoxy-ethyl) ether; diisopropyl ketone and phenylethyl acetate are preferred. The preferred ratio of the alkylaluminum compound to reaction rate moderator can range from about 0.2 to about 3.5 on a molar basis. The metathesis polymerization reaction is temperature-dependent; the reaction rate increases with increasing temperature. Generally, the reaction mixture of parts (A) and (B) (and (C)) of the catalyst system can be cooled or heated to polymerization temperature at the start of the mixing or at any point during the addition of the various reactants and components of the catalyst system. The following examples more fully illustrate a preferred embodiment of this invention. EXAMPLES I - VIII The following examples illustrate metathesis catalyst polymerized poly(dicyclopentadiene) matrixes having incorporated therein preferred sterically hindered phenolic-aryl amine antioxidant compositions of the present invention that provide for unexpectedly increased polymer oxidative stability relative to the poor oxidation protection demonstrated by currently available antioxidants when used alone. In Examples I - V, a three-stream RIM process comprising parts (A), (B) and (C) is employed to prepare samples of poly(dicyclopentadiene) having incorporated therein the indicated antioxidant systems which are then tested for antioxidant activity, as summarized in Table I below. Example Type Aryl amine/Phenol Mole % PDSC (°C) PDSC Induction Time (min. @ 38 bar (550 psi)) Aryl amine Phenol I DPA/Irganox 1035 0.78 0.10 130 70 DPA 0.88 30 Irganox 1035 0.88 47 II DPA/Irganox 1035 0.78 0.21 150 37 DPA 0.98 10 Irganox 1035 0.98 20 III DPA/Irganox 259 0.78 0.21 130 93 DPA 0.99 45 Irganox 259 0.99 52 IV DPA/Ethyl 702 0.78 0.20 130 66 DPA 0.98 45 Ethyl 702 0.98 22 V DPPD/Irganox 1035 0.51 0.21 130 72 DPPD 0.72 57 Irganox 1035 0.72 28 VI Stalite S/Irganox 1035 1.0 1.1 150 12 Stalite S 1.1 8.5 Irganox 1035 1.1 6 VII Stalite/Irganox 1035 1.0 0.1 150 12 Stalite 1.1 3 Irganox 1035 1.1 6 Preparation of part (A): A 0.5 molar solution of tungsten catalyst is prepared by adding 100 grams of WCl₆ to 60 milliliters of dry toluene under a nitrogen atmosphere, followed by the addition of a solution of 41 grams of paratertiarybutylphenol(t-BuOH) in 30 milliliters of toluene. The catalyst solution is sparged overnight with nitrogen to remove traces of HCl. Next, 0.44 milliliters of the tungsten catalyst solution prepared above is syringed into a sparged airtight bottle containing 20 milliliters of dicyclopentadiene that has been purified according to the procedure as set forth in U.S. Patent No. 4,400,340. Preparation of part (B): A 1.0 molar activator monomer solution is prepared by combining, under a blanket nitrogen atmosphere, dicyclopentadiene and a mixture of tri-N-octyl aluminum (TNOA) and dioctylaluminum iodide (DOAI) in a 85/15 molar ratio. A reaction moderator, diglime (DY) is then added to achieve a 85/15/100 molar ratio of TNOA/DOAI/DY. Next, 0.34 milliliters of activator monomer solution prepared above is syringed into a sparged airtight bottle containing 20 milliliters of purified dicyclopentadiene. Preparation of part (C): A third stream is prepared that contains the indicated sterically hindered phenolic-aryl amine antioxidant compositions or comparative antioxidants and dicyclopentadiene. A mixture of the indicated sterically hindered phenolic and aryl amine compounds is prepared in the desired molar ratio, then added to a sparged airtight bottle containing 20 milliliters of dicyclopentadiene. Solutions of comparative antioxidants used alone and polymerizable monomer are prepared in similar fashion. Polymerization of dicyclopentadiene monomer is then accomplished by simultaneously injecting two milliliters of each component, (A), (B), and (C), into a common mixing vessel that flows into a reaction vessel. After metathesis catalyst polymerization of the monomer mixtures of components (A), (B), and (C), above, the effect on oxidative stability of the resulting poly(dicyclopentadiene) matrix by the various sterically hindered phenolic-aryl amine antioxidant compositions and comparative antioxidants incorporated therein is determined using high pressure differential scanning calorimetry (PDSC). Such a technique is described, for example, in 91 Themochimica Acta 87-94 (1985) and in Proceedings of the 13th North American Thermal Analysis Society, Philadelphia, PA. p. 520 (1984). Using this technique, the time taken for a given sample to begin the process of autooxidation at a constant temperature, as exhibited by a sudden exothermic reaction, is measured. The results, as summarized above in Table I, illustrate the unexpected increased oxidative stability (PDSC induction time as a measure of minutes) of the poly(dicyclopentadiene) matrix achieved for a given molar ratio of antioxidant compositions of the present invention.

Claims: a composition polymerizable by a ring-opening metathesis-catalyst, comprising dicyclopentadiene or another norbornene-type monomer and a sterically hindered phenolic compound as an antioxidant stabilizer, characterized in that the stabilizer is a synergistic antioxidant mixture that is compatible with polyunsaturated hydrocarbon polymers and comprises: (a) a sterically hindered phenolic compound having one of the following general formulas: in which A represents a mono or polyvalent organic radical selected from a straight-chain or branched C₁ to C₂₀-saturated aliphatic group, a straight-chain or branched C₂ to C₂₀-unsaturated aliphatic group, an aryl group, a C₇ to C₂₀-aralkyl group, or a C₇ to C₂₀-aralkenyl group; and m represents a positive integer from 0-20, and n represents a positive integer from 1-20, and p and q each represent a positive integer from 1-4; or 4-hydroxymethyl-2,6-ditertiarybutyl phenol or thiodiethylene bis (3,5-ditertiarybutyl-4-hydroxyl)-hydro cinnamate and (b) at least one aryl amine compound having one of the following general formulas: in which R₁ and R₂ are the same of different aryl groups in which R₃ and R₄ are the same or different and can be hydrogen atoms, or straight-chain or branched C₁ to C₂₀-alkyl groups, straight-chain or branched C₂ to C₂₀-alkylene groups, aryl groups, C₇ to C₂₀-aralkyl groups or a C₇ to C₂₀-aralkenyl groups, or radicals having one of the following formulas: in which n represents a positive integer from 1-20, the sterically hindered phenolic compound and aryl amine compound being present in a molar ratio ranging from about 0.1 to about 10. A ring-opening metathesis-catalyst-polymerizable composition as claimed in claim 1, further characterized in that the phenolic compound is thiodiethylene bis(3,5-ditertiarybutyl-4-hydroxyl)-hydro-cinnamate, and the aryl amine compound is diphenylamine. A ring-opening metathesis-catalyst-polymerizable composition as claimed in claim 1, further characterized in that it includes dicyclopentadiene and another norbornene-type monomer. A metathesis catalyst polymerizable composition as claimed in claim 3 wherein the sterically hindered phenolic-aryl amine antioxidant composition is in an amount ranging from about 0.25 to about 4 parts per 100 parts by weight of the polymerizable monomeric content.

Inventors: PAISNER, MARTIN J.
Applicants: HERCULES INCORPORATED
Application year: 1988
Main classification: C08K5
IPC codes: C08K5, C08L65, C08G61