Title of Invention

METHYLMETHACRYLATE-BUTADIENE-STYRENE GRAFT COPOLYMER COMPOSITION STABLILZED AGAINST THERMAL OXIDATION

Abstract

ABSTRACT METHYLMETHACRYLATE - BUTADIENE - STYRENE GRAFT COPOLYMER COMPOSITION STABLILZED AGAINST THERMAL OXIDATION 823/CHENP/20Q6 The present invention relates to a polymer composition stabilized against thermal oxidation comprising a) a polymer, which is a graft copolymer of methylmethacrylate and styrene on polybutadiene or polybutadiene-styrene (methylmethacrylate-styrene-butadiene graft copolymer MBS); b) a sterically hindered phenolic antioxidant of formula (I), (II) or (III) or a mixture thereof in an amount of 0.05 to 1% based on the weight of the dry graft copolymer components as herein described and c) a thioether differing from that of formula (II) in an amount of 0.1 to 5% based on the weight of the dry graft copolymer component a). This invention also relates to a process for the stabilization of graft copolymers.

Full Text

Stabilization of Methvlmethacrvlate-Butadiene-Stvrene Graft Copolvmers against Thermal Oxidation The instant invention relates to a stabilized composition of methylmethacrylate-butadiene-styrene graft copolymers with selected sterically hindered phenolic antioxidants and thioethers. Further subjects of the invention are a process for the stabilization of methylmethacrylate-butadiene-styrene graft copolymers and the use of selected sterically hindered phenolic antioxidants together with a thioether for the thermal stabilization of said graft copolymer. Polymers having a grafted polybutadiene or polybutadiene-styrene rubber phase, such as ABS (acrylonitrile-butadiene-styrene), or MBS (methylmethacrylate-butadiene-styrene) are very prone to oxidative degradation of the rubber phase, especially under the influence of heat and oxygen. This is especially problematic during air-drying of ABS- or MBS-graft-phase powders. MBS is even more prone to oxidation and, therefore, more difficult to stabilize because it has usually a higher rubber content than ABS, and a smaller particle size of the graft-phase powder (higher surface area). The stability of MBS powder is generally much lower than that of ABS. State of the art in the stabilization of MBS against thermal oxidation, is the use of combinations of hindered phenolic antioxidants in combination with thioethers. Typical hindered phenolic antioxidants are, BHT, ©Topanol CA, ®CIBA ©Irganox 1076, ®CIBA ©Irganox 245, ®CIBA ©Irganox 1141, etc. As thioethers, usually DLTDP (dMauryl-thio-di-propionate) or DSTDP (di-stearyl-thio-di-propionate) are used. To adequately protect the MBS during the drying step, much higher concentrations of these stabilizers have to be used than in ABS. However, very high concentrations of hindered phenolic antioxidants and thioethers can lead to color formation during processing and end use, due to over-oxidation of the hindered phenolic antjoxidants and subsequent formation of highly colored quinoid structures. Therefore, more efficient stabilizer packages for MBS are required that do not need such a high dosage. Surprisingly it has been found that some very specific hindered phenolic antioxidants, such as ©Wingstay L, ®CIBA ©Irganox 415 or ®CIBA ©Irganox 3790 show especially good performance in MBS versus the above mentioned prior art stabilizers. Although the excellent performance of ®Wingstay L and ®CIBA ©Irganox 415 is well established in ABS, so far neither ®Wingstay L, ®CIBA ®lrganox 415 nor ®CIBA ®lrganox 3790, have been used for pure MBS stabilization. Although MBS seems to be a simitar polymer as ABS, it nevertheless behaves very differently in terms of stabilization against thermal oxidation. Besides the above already mentioned, generally much lower thermal stability of MBS compared to ABS, the following differences are noteworthy. ABS can be stabilized with hindered phenol antioxidants alone, or with combinations of hindered phenol antioxidants and thioethers (DLTDP, DSTDP). MBS, on the other hand, cannot be stabilized with hindered phenol antioxidants alone. Only combinations with thioethers provide sufficient stability. In view of the considerable differences between MBS and ABS, it is surprising that combinations of ©Wingstay L, ®CIBA ©Irganox 415, or ®CIBA ©Irganox 3790 and thioethers show the best performance in MBS. One aspect of the invention is a stabilized polymer composition comprising a) a polymer, which is a graft copolymer of methylmethacrylate and styrene on polybutadiene or polybutadiene-styrene (methylmethacrylate-styrene-butadiene graft copolymer MBS); b) a sterically hindered phenolic antioxidant of formula (I), (II) or (III) or a mixture thereof and c) a thioether differing from that of formula (II); with the proviso, that no other styrene polymer or copolymer, which is not a graft copoiymer on butadiene is present. MBS is a commercial graft latex, which can, for example, be prepared according to EP 0 488 550. The above stabilized polymer composition may be in the form of a latex, i. e. the composition contains a water phase. Preferably the stabilized polymer composition is, however, in the solid state. For instance the stabilized polymer composition is in the form of a powder or granulate. The compounds according to formulae (I), (II) and (III) are commercial compounds. The compound of formula (I) is bis(3-tert-butyl-4-hydroxy-5-methyl-phenyl)dicyclopentadiene commercialised as Wingstay® L from Eliokem or Ralox® LC from Raschig. In the commercial compounds the mean value of n in formula (I) is approximately 1. The compound of formula (II) is 4.41 thiobis(6-tert-butyl-3-methylphenol), commercialised as ®CIBA ©Irganox 415 from Ciba Specialty Chemicals Inc. The compound of formula (III) is 1,3.5-tris [4-(1,1-dimethylethyl)-3-hydroxy-2l6-dimethylphen yl] methyl]-1.3,5 -triazine-2A6(1H,3H,5H)-trione, or 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate commercialized as ®CIBA ©Irganox 3790 from Ciba Specialty Chemicals Inc. The compound of formula (I) is most preferred. In a specific embodiment the thioether is a compound of formula (IV) or (V) wherein the Ri are independently Cg-Caoalkyl. Specific compounds according to formula (IV) are di-lauryl-thio-di-propionate and di stearyl-thio-di-propionate, which are commercial products of Ciba Specialty Chemicals Inc. with the trade names ®CIBA Irganox® PS 800 and ©CIBA Irganox® PS 802. The compound of formula (V) with Ri = C8alkyl is also a commercial product of Ciba Specialty Chemicals Inc. and sold under the trade name ®CIBA Irganox® 1520. For example the sterically hindered phenolic antioxidant is present in an amount of 0.05 to 1 % based on the weight of the dry graft copolymer, component a). For instance the thibether is present in an amount of 0.1 to 5%, preferably from 0.1 to 3% based on the weight of the dry graft copolymer, component a). Preferably the ratio of sterically hindered phenolic antioxidant to thioether is from 1:1 to 1:5, more preferably from 1:2 to 1:4. In a specific embodiment the stabilized polymer composition comprises additionally a further sterically hindered phenolic antioxidant different from those of formulae (I), (II) or (III), a phosphite process stabilizer, a UV-absorber, a sterically hindered amine light stabilizer, a metal deactivator, an acid scavenger, a metal salt of a fatty acid, a fluorescent whitening agent, a biocide or a surfactant. Examples of the additional components are given below. 300; [R-C^CHJ—COO-CHJCHJ}- , where R = S’-tert-butyM’-hydroxy-S’^H-benzotri- azol-2-ylphenyi, 2-[2l4iydroxy-34a,a^imethylbenzyl)-5l-(1l1,3,3-tetramethylbutyl)^ benzotriazole; 2-[2l-hydroxy-3l-(1,1,3,3-tetramethylbuty!)-5f-(oc,a-dimethylbenzyl)phenyl]ben-zotriazole. 2.2. 2-Hvdroxvbenzophenones. for example the 4-hydroxy, 4-methoxy, 4-octyloxyf 4-decyl- oxy, 4-dodecyloxy, 4-benzyloxy, 4,2\4l-trihydroxy and 2l-hydroxy-4(4l-dimethoxy derivatives. 2.3. Esters of substituted and unsubstituted benzoic acids, for example 4-tert-butylphenyl salicylate, phenyl salicylate, octylphenyl salicylate, dibenzoyl resorcinol, bis(4-tert-butylben- zoyl)resorcinol, benzoyl resorcinol, 2,4-di-tert-butylphenyl 3,5-di-tert-butyl-4-hydroxybenzo- Fillers and reinforcing agents, for example calcium carbonate, silicates, glass fibres, glass bulbs, asbestos, talc, kaolin, mica, barium sulfate, metal oxides and hydroxides, carbon black, graphite, wood flour and flours or fibers of other natural products, synthetic fibers. 11. Other additives, for example plasticisers, lubricants, emulsifiers, pigments, rheology additives, catalysts, flow-control agents, optical brighteners, flameproofing agents, antistatic agents and blowing agents. 6b. Hydrogenated aromatic polymers derived from hydrogenation of polymers mentioned under 6.), especially including polycyclohexylethylene (PCHE) prepared by hydrogenating atactic polystyrene, often referred to as polyvinylcyclohexane (PVCH). 6c. Hydrogenated aromatic polymers derived from hydrogenation of polymers mentioned under 6a.). Homopolymers and copolymers may have any stereostructure including syndiotactic, isotao tic, hemi-isotactic or atactic; where atactic polymers are preferred. Stereoblock polymers are also included. 7. Halogen-containing polymers such as pofychloroprene, chlorinated rubbers, chlorinated and brominated copolymer of isobutylene-isoprene (halobutyl rubber), chlorinated or suffo- chlorinated polyethylene, copolymers of ethylene and chlorinated ethylene, epichlorohydrin homo- and copolymers, especially polymers of halogen-containing vinyl compounds, for example polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, as well as copolymers thereof such as vinyl chloride/vinylidene chloride, vinyl chloride/vinyl acetate or vinylidene chloride/vinyl acetate copolymers. 8. Polymers derived from a,{5-unsaturated acids and derivatives thereof such as polyacry- lates and polymethacrylates; polymethyl methacrylates, polyacrylamides and polyacryloni- triles, impact-modified with butyl acrylate. 9. Copolymers of the monomers mentioned under 9) with each other or with other unsatu- rated monomers, for example acrylonitrile/ butadiene copolymers, acrylonitrile/alkyl acrylate copolymers, acrylonitrile/alkoxyalkyl acrylate or acrylonitrile/vinyl halide copolymers or acry lonitrile/ alkyl methacrylate/butadiene terpolymers. 10. Polymers derived from unsaturated alcohols and amines or the acyl derivatives or ace- tals thereof, for example polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, polyvinyl benzoate, polyvinyl maleate, polyvinyl butyral, polyallyl phthalate or polyailyl melamine; as well as their copolymers with olefins mentioned in 1) above. 11. Homopolymers and copofymers of cyclic ethers such as polyalkylene glycols, polyethy lene oxide, polypropylene oxide or copolymers thereof with bisglycidyl ethers. 12. Polyacetals such as polyoxymethylene and those polyoxymethylenes which contain ethylene oxide as a comonomer. 13. Polyphenylene oxides and sulfides, and mixtures of polyphenylene oxides with styrene polymers or polyamides. 14. Polyurethanes derived from hydroxyl-terminated polyethers, polyesters or polybutadi- enes on the one hand and aliphatic or aromatic polyisocyanates on the other, as well as precursors thereof. 15. Polyamides and copolyamides derived from diamines and dicarboxylic acids and/or from aminocarboxylic acids or the corresponding lactams, for example polyamide 4, polyamide 6, polyamide 6/6, 6/10, 6/9, 6/12, 4/6, 12/12, polyamide 11, polyamide 12, aromatic polyamides starting from m-xylene diamine and adipic acid; polyamides prepared from hexamethylenediamine and isophthalic or/and terephthalic acid and with or without an ela stomer as modifier, for example poIy^^A-trimethylhexamethylene terephthalamide or poly- m-phenylene isophthalamide; and also block copolymers of the aforementioned polyamides with polyolefins, olefin copolymers, ionomers or chemically bonded or grafted elastomers; or with polyethers, e.g. with polyethylene glycol, polypropylene glycol or polytetramethylene glycol; as well as polyamides or copolyamides modified with EPDM or ABS; and polyamides condensed during processing (RIM polyamide systems). 16. Polyureas, polyimides, polyamide-imides, polyetherimids, polyesterimids, polyhydantoins and polybenzimidazoles. 17. Polyesters derived from dicarboxylic acids and diols and/or from hydroxycarboxylic acids or the corresponding lactones, for example polyethylene terephthalate, polybutylene tereph- thalate, poly-1,4-dimethylolcyclohexane terephthalate, polyalkylene naphthalate (PAN) and polyhydroxybenzoates, as well as block copolyether esters derived from hydroxyl-terminated polyethers; and also polyesters modified with polycarbonates or MBS. is reached is determined. The exothermic reaction, which occurs, is a measure of the degradation of the polymer. The stabilization of the different MBS powders obtained, and their thermal stability is shown in Table 1 ** thermal stability DSC, 180°C, oxygen, aluminum cups: minutes to the maximum of the exotherm. ***Comparative example 1 is coagulated with 1.21% sulfuric acid (6.8g 10% sulfuric acid) based on dry MBS.

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