[1]Uni'ted States Patent Office 3,189@630 3,189,630 LANT-'k'IANIDE AL@X"(LA@TED LYDROXYBEI,4ZOATES Edgar J. Smutuy, San r4rancisco, Ca!if., assigner to Shell Oil Company, New YoeLE, N.Y., a corporalion of Delaware No Drawin,-. Filed Oct. 18, 1962, Ser. No. 231,560 3 Clmms. (C]. 260-429.2) INTRODUCTION This invention relates to novel metal salts, and to their use as stabilizers for polymers. More particularly, the invention relates to ipetal salts of certain hy&oxybenzoic acids, and to their use as stabilizers in polymenc olefin resins. It is kno-,vn that actinic rad,ation, particularly in the near ultraviolet region, has a deleteriotis effect on both the app-@arance and properties of organic polymers. For exan-iple, normary colorless or light-colored pc)lyesters yellow on expostire to sunlight, as do such cellulosies as cellulose acetate. Polystyrene discolors and cracks, with accompanyin.- loss of ;ts desirable physicil properties when exposed to actinic liaht, vvhile vinyl resins, such as vinyl chloride and vinyl acetate s,7)ot and de.-rade. Tl@le rate of air oxida' Lion of polyolefins such as polyethylene and polypropylene is mater@ially a.-celerated by ultravio' et light. Such compounds as the hydrox@,b.nzoph-.nones ha-ve been used to stabilize the polymers agoinst det--rioration. NVhile many organic comnoil-nds, including benzopiienones and their allylated hoirolo.- s, ire liseful as actiliic stabilizers in resins, the effect of these stabilizers tends to be transi-.nt. In man3r cases, heatin.- of the stabilized polymer in the course of fabr,@eation or use volatiiizes some or aH of the stabilizer. Similirly, treatment of the stabilized polymer with solver@, such as hydrocarbons leaches the stabilizer out of the 'rsesin. In either instance, the resulting polyrner issubstantially less resistant to actinic d-,gradation. T-he present invent-@on is d@'@rected to a class of hght stabilizers which is sutbstantially less volatile and more resistant to leachin- than are the stabilizers of the art. Furthermore, not only are many of tac conipounds of the instant invention excellent li,@ht stabilizers, but some of them are also si,-perior antioxidants. OBJECTS It is an object of the pres.-nt invention to provide ilo'vel iretal salts of certain allylaled hydroxybenzoic acids, useful as antioxl:dants of actinic stabil-@Zers in plastics. Anoth,r object of the inventioii is 'Lhe provision of plastic com-oositions stabilized with such Paetal salts. The novel class of rare earth salts of certain 3,5-dialkyl-4-hydroxybenzoic acids is another object of the invention. Other objects wil'i be apparent @krom the follionviiig detailed description of the invention. SALTS The metal salts of tii.- invention are those of 3,5 -diall,,yl4-hydroxybenzoic acld, Vnerein each alkyl group has UP to 8 carbon atoms and ,it least one alicyl group is branched on the alpha carbon atom. These salts preferably have thestructuro OTT R c-o-m where each R is alkyl of up to 8 carbon atoms, M is an Patented June 15, 1965 2 n-valent metal, ajid n is a positive integer, By metal is meant an electropositive chemical element characterized by its condlictivity of heat @ind electricity at standard condit@ions cf temperatiire and pressure. Examples of the alkali metal salts of the 3,5-dia lkyl-4hydroxybenzoic acids include sodium 3,5-di-tert-butyl-4- hydroxvbenzoate; potassitim 3,5-diisopropyl-4-hydioxybenzoate; and lithium 3,5@di-tert-amyl-4-hydroxybenzoa@te. AlkaLne earth benzoates include magnesium 3-met-hyl10 5-tert-butyl-4-hydroxybenzoate; calcium 3-ethyl5-isopropyl-4-hydroxybenzoate; and bariu.-n 315-di-tert-butyl-4hydroxybenzoate. Salts of metals of Groiip IIIA of thi,@ Merideleef Periodic Table are exe@mplified by aluminum 3,5-ch@tertbutyl4-hydroxybenzoate and yttrium 3,5@di15 tert-a@nyl-4@hydroxybenzoate. Salts of metals from ot@her groups !of that table include copper 3,5-di-tertbutyl-4hydroxybenzoate; manganese 3,5-disec@butyl-4-hydroxybenzoate; and zinc 3,5-dicylcloh exyl-4-hydroxybenzoate. Parbic-alarly effective as light stabilizers in polyolefins are the par@amagnet;C salts of 3,5-dialkyl-4-hydroxybenzoic acids. These are the salts of transition metals and of rare earths. Examloles of the transit@;.on metal salts are iron 3,5-di-t@-r-t-hoxyl-4-hydroxybenzoate, cobalt 3,5-diisopropyl-4- hyd@roxybenzoate; and nielcel 3-methyl-5@iso2 propyl-4-hychoxybenzoate. By rare eart,'Ai metal salts are meant the salts of metals of tne lanthanide series, those metals of qtomic number 57 th-rou.-h 71. Si-ich salts includes cerium 3,5-ditertbutyl-4-liydroxybenzoate; praseodymiuin 3,5-diisopropyl30 4.,hydroxybenzoate; neodyr@iilun 3-,isopropyl-5- tert-butyl4-hydroxybenzoate; samarii,-in 3,5-di-see-butyl-4-hydroxybenzoa-t@-; europium 3,5-di-,sec-hex3il-4-hydroxybenzoate, gadoiiniwn 315-di-tert-amyl-4-hydroxybenzoate; dysprosilim 3,5@di-tert-@butyl-4@hydroxyb-,nzoate; erbium 3,5- 35 diisr,,propyl-4-hydroxyberizoate; and lutetilml 3-isopropyl5-tert-a-myl-4- hydroxybenzoate. These salts, in their pare form, are white or lightcolored crystalline solids. They are readily compatible with solid resinous plastics, and may be incorporated 40 therein by milling or other conventional methods. PREPARATION The met-al salts of @the @particular 3,5-dialkyl-4- hydroxybenzo-'c acids of the iiivention are prepared by reaction 15 @of 3,@.di.,Ilyl-4@hydroxyberzoic !acid and a basic metal corinpound. The 3,5-dialkyl-4-hydroxybenzoic acid from which the salt is prepared prefere@bly has the structtire OH 50 RC=O I 55 UhL wherein each R is alkyl of up to 9 carbon atoms and at least @one alkyl group is branched on the alpha carbon a,toni, that is, a @secondary or tertiary lalkyl radical. If 'desired, the -dialkyl@hydroxybenzoic acid n-iay have, one 60 or both o'L t@ic remaining rin.- positions -alkylated, preferably @vith methyl groups. Examples of such acids are 3-methyl-5-diisopropyl-4hydroxybenzoic @acid; 3,5 - diisopropyl - 4 - hydroxy65 benzoic acid; 3 - isopropyl - 5 - tert - butyl - 4 -- hydroxybenzoic acid; 3,5 - di - @cyclohexyl - 4 - hydroxybenzoic -acid; 3,5 - di - see - butyl - 4 - hydroxybenzoic acid; ,and 2,4 - diniethyl - 3,5 - di - tert - butyl - 4 - hydroxybenzoic jacid. 70 -,@"articiil-arly preferrpd arids are thos@@ in W'rlich eavh 'of t@e allyl groups ortho to the -alkyl g@-oups is tertiary, since these acids are those whereinthe phenolic hydroxyl
[2]3 group is the niost smelded from reaction. Examples of such acids are 3,5-di-tert-butyl4-hydroxybenzoic acid; 3,5-di-tert-amyl-4-hydroxybenzoic acid; and 3,5-di-tert,octyl-4- hydroxybenzoic acid. To form the salt of the invenf@ion, the acid described is raacted with a basic metal,compound. By basif, metal compound is meant a compound which, in iaqueous solution, would give the -resulting sblution a pH greater than 7. Since compounds include the -bydroxides of r@ietals, such as sodium hydrox@ide and potassium hydroxide; or the salts of such metals with weak acids, such as calci-Lim carbonate or magnesiu-m carbonate; or c--rium acetate, europium acetate, dysprosium aep-tate,, sodium acetate, ox the like. The reaction is conducted in liquid phase by conventional methods. For example, -the alkali metal salt of the acid is xea:dily -prep!ared bydissolving solid 3,5-dialkyl-4- @hydroxybenzoiG acid in aqueous base,and recovering the resulting salt. Alternatively, the acid may be refluxed in an inert organic solvent with the appropriate metal acetate while azeotroping off the acetic acid-solvent azeotrope. A stoichiometric excess of @either the ,acid or the basic icompound may be employed, but, since the xeaction is substantially quantita-tive, only a slight excess of either Teactant is requir6d. The preparation ,of the salt may be conducted at any convenient temperature, 'Lemperatures batween about O' C. and about 150' C. being preferred. The resulting salts may readily be recovered by sepa-rating the solvent and reagtants from the product by ,disLilla,tion, extraction, crystallization or the like. Since ,the salts iare definite crystalline metal compounds, they maY be recovered and purified by these methods or by ,their combination. For example, when 3,5- diisopropyl4@hydroxybenzoic -acid is dissolved in 10% aqueous potassium -carbonate, the resulting potassium 3,5-diisopropyl-4-hydroxybe,nzoate is recovered by cooling the Teaclion mixture until the metal salt crystallizes, andrecovering the resulting needlelike crystals. The produot may, in turn, be washed or reerystahized v;ith water or other,appropriate solvents. COM,POSIT.IONS It is a surprising and advantageous feature of the invention that the metal sal-ts described act as stabilizers for polyolefins. In general, it has been observed that traces of metals and of metal salts in such polyolefins as polyethylene and polypropylene act as pro-oxidants ? ,and considerable effort is employed to separate such materials from the xesin. However, it has been found that -the metal salts of the3,5-di-alkyl-4-,hydroxy@benzoic acids ,described iact @as sta:bilizers for polyolefins,- enhancin.their @stability to therma:l and ultraviolet degradation. The salts lof the invention are generally useful as actinic sta:bilizers in all solid synthetic organic plastics normally subject to @actinic degradation. Exemplary of such plastics are the, polyvinyl resins, such as polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, polystyrene, and the acryl-ates and mothaerylates, such -as polymetayl methacrylate. T,he prcf--rred class of plastics in the composi@tions of the invention, however, are the polyolefins. The polymers of alpha-olefins stabilized by the compounds of the invention are those normally solid hydrocarbon poly-meric materials which are;obtained by polymerizing such_ monoolefins @as etliylene; propylene; butene-1; pentene-1; 3-- methyl-butene-1; hexene-1; 4-me @thyl-pentene-1; 4-methyl--hexene-1; 4,4- dimethyl-pentche-1; and the lil,,e, as weU as their icopolymers, e.g., ethylen@- propylene copolymers and the like. Polymers of alefms having-up -to 8,oarbon atoms are the preferred species. Particularly preferred polym&rs for the compositions of this invention are those normally solid polymers Of 3,189,630 4 alnha-olefins having up tothlee ca:rbon -atoms, e.g., ethylene @and propylene, and their copolymers. The stabilized polymeric compositions of the invention are those comprisin@ a rnajor amount of a resin such as those described above in intimate admixture with a metal salt of 3,5-dialkyl-4- hydroxybenzoic acid. The salt is readily incorporated in the resin to afford a stable homogeneous composition. For example, mechanical methods such as Banburying or hot milling, may be employed to 10 combine the stabilizer with the solid re-qin. Where the polymer is prepared from a liquid monomer, as in the case of styrene or methyl methacrylate, the stabilizer may be dispersed or dissolved in the r@ionomer prior topolymerization or curing. 15 Only sufficient stabilizer is required to stabilize the polymer against actinic degradation. Depending on the nature of the polyn-ler, the particular stabilizer employed, and the severity of exposure of the resulting composition, from about 0.001% to 10% by weight of the stabilizer 20 based on the polymer@ will be required. In most cases, however, from about 0. I % to about I % on the same basis will be sufiqcient. In addition to tbe actinic stabilizers described, the plastic compositions may contain other additives such as 2,5 plasticizers, pigments, fillers, dyes, glass or other fibers, thermal antioxidants, and the like. For example, in most applications, it will be desirabl@- to incorporate into the resin compositions sufficient thermal antioxidant to protect the plastic a.-ainst thermal and ioxidative degradation. 30 The amount of antioxidant required wiR be comparable to that of the actinic stabilizer, i.e., from about 0.001% to abolit 10% by weight, based on the polymer. Representative of such antioxidants are amino compounds such as diisopropanolamine; p-phenylene diamine and durene 35 diamine; phosphite esters, such as triphenyl phosphite and dibutyl phospmte and alkyl aryl phosphites such as dibutyl phe-@lyl phosphite, and the like. The best results are obtained with the preferred class of thermal antioxidants, the hindered phenols. These com40 pounds have been found to provide the best thermal stabilization with the least attendant discoloration in the compositions of the invention. These phenols may be mononuclear, as in the case of 2,6-di-tert-butylphenol;- 2,6-diter'L-butyl - 4 - methylphenol; 2,6-diisopropyl-4-methoxy45 methylphenol; 2,6 - di-tert-butyl-4-hydroxymethyl-phenol; and 2,4-dimethyl-6-tertbutylphenol; or they may be polynuclear Particularly preferred polynuclear phenols are the bi@henols, such as 3,3',5,5'-tetratert-butyl-biphenol and 3,3',5,5'- tetraisopropyl-biphenol; and such bisphenols as bis (3,5-di-tert-butyl-,Ibydroxyphenyl)methane; bis(3- 50 tert-butyl-5-methyl-2-hydroxyphenyl)methane; and bis(3- tert - butyl - 5-methyl-2-hydroxyphenyl) sulfide. Other PolYnuclear Phenolic compounds which are effective antioxidants include the bis(3- dialkyl-4-hydroxybenzyl) durenes, such as bis(@,5-di-tert-butyl-4-hydroxybenzyl)du55 rene; th,,- polypbenolic phenols, such as 2,4,6-tri s(3,5-ditert-amyl - 4 - hydroxybenzyl)phenol; such polyphenolic benzenes as 1,3,5-trimethyl-2,4,6- tris(3,5-di-tert-butyl-4hydroxybenzyl) berizene; and the di (3,5-dialkyl-4- hydroxy60 benzyl) polynuclear aromatics, such as 9,10-bis( 3,5-ditert-butyl-4-hydroxybenzyl) anthracene and 1,4-bis(3,5diisopropyl-4-hydroxybenzyl) naphthalene. Plastic compositions consisting essentially of a solid organic polymeric material of the type described and containing stabilizing amou-.its of the metal 3,5-dialkyl4-hy65 droxy@benzoate actinic stabilizer and of the phenolic antioxidatits described are characterized by extreme phy,,ical and chemical durability at elevated tem cratures and ex. p tended exposures to ultraviolet rad@'.ation. - Furthermore, 70 light colored or transparent resinous products of thece compos;tions do not change color under even the most severe conditions of use. The following examples v@ill illustrate the nature and advantages of thpcompositions of the invention. it 75 should be understood, however, that the -examples are
[3]merily illustrative, and are not to be regarded as limitations to the appended claims, since the basic teachings th@-reof may be varied at wiH, as will be understood by one skilled in the art. E.Ta@tzple 1 5 Sodium 3,5-di-tert-butyl-4-hydroxybenzoate was prepared by dissolving 3,5-ditert-butyl-4-hydroxybenzoic acid in a 10% w. aqueous solution of sodium carbonate. The resulting react@@On mixture was extracted with carbon 10 tetrachloride to remove insoluble components, and the yellow-,-reen aqueous solution cooled until the pale yellow needle-like crystals of sodium 3 ,5-di-tert-butyl-4-hydroxybenzoate precipitated. The needles were recrystallized from water. 15 Example 11 5 grams of 3,5-di-tert-butyl-4-hydroxy'oenzoic acid were dissolved in 100 cc. of water containing 1.1 .-rams of copper carbonate, the mixture bein.a maintain,-d under ni- 20 trogen and held at about 90' C. for 168 hours. At the end of that time sodiun carbonate was added to neutralize the excess acid and the nlixture cooled. The copper benzoate was precipitated, washed and dried to afford 4.5 grams of Exan?ple III With 10 grams of 3,5-di-ter t-butyl-4-hydroxybenzoic acid was reacted from 4 to 5 grams of each of the follow- 30 ing metal acetates. Each reaction was conducted in about 200 cc. of xylene under nitrogen; the reaction mixture was held at a temperature such that the xylene-acetic aeid azeotrope was continuously removed. At the end of tfic reaction, when acetic acid ceased to come over, the sol- 35 vent was flashed off under reduced pressure and the metal 3,5-di-tert-butyl-4-hydroxybenzoate recovered. The exp.-rimental data are summarized below: 40 U ! A B L B I H o u r s t o Salt (0.5% w.): Failure, 133' C. None --------- --------- --------- --------- 290 Sodiu m 3 ' 5- ditertbutyl4- hydro xyben zoate --- 350 Nickel 3,5-ditertbutyl4- hydro xyben zoate ---- 480 Basic alumin um 3,5-ditertbutyl4- hydro xyben zoat e ------ ------ ------ ------ ------ 300 Example V In the outdoor exposure test, five mil film samples of the same polypropylene as in the previous example were exposed on the laboratory at Emeryville, California, and to Arizona sun, and periodically tested by bending through 180'. The number of weeks required before the fums so tested snapped on bending is shown in the table. It will be seen that the sodium salt compound increased the weather stability of the polypropylene materially. TABL EII Additi ve (0.5% w.) Eineryvil le Arizona, Roof, Weeks Weeks None ------------ ------------------------- 3.5 8.5 Sodium 3,5-ditort-butyl-4-hydroxycopper 3,5-di-tert-butyl-4-hydroxybenzoate. 2,5 benzoate ------------------ -------------- 9.5 16.5 Example VI In the accelerated Fade-Ometer test, the conventional Atlas Weatherometer wherein the arc light source has been supplemented by addition of eight fluorescent ultraviolet light sources, aR film samples tested pass within a quarter inch of the light sources. It has been found that in this accelerated exposure test, conditions are approximately eight times as stringent as in the unmodified Weatherometer. It viill be seen from the table that under these extreme conditions use of the salts of the invention more than doubles the ultraviolet light stability of the polypropylene. The resulting data were obtained using polypropylene samples containing in addition to the me-tal salt evaluated, 0.2% w. of bis(3,5-di-tert-bu,yl-4- hydroxybenzyl)durene Acetate 3,5-Di-tert-butyl-4-hydroxy. as thermal antioxidant. Benzoate Salt Fade-Ometer, Wt., g. Wt., g. 45 Salt: None days ---------------------------------- 41/2 Sodium 3,5-di-tert-butyl-4-hydroxybenzoate -- 121/z Ce(AC)4 ------------------ 3.9 Ce -------------------- 9.0 Manganese 3,5-di - tert-butyl - 4 - hydroxybenLa(AC)3 ------------------ 4.35 La -------------------- 12.6 Sm(Ac)3 ----------------- 4.54 Sra ------------------- 12.1 zoate -------------------------------- 121/2 Gd(Ac)3 ----------------- 4.65 Gd ------------------- 12.4 Nickel 3,5-di-tert-butyl-4-hydroxybenzoate --- 14 Er(Ac)3 ------------------ 4.75 Er -------------------- 12.3 50 Copper 3,5-di-tert-butyl-4- hydroxybenzoate -- 101/2 Dy(Ac)3 ----------------- 467 Dy ------------------- 12.4 Nd(Ac) ---------- ------ @. 42 Nd ------------------- 12.7 Cobalt 3,5-di-tert-butyl-4-hydrozybenzoate --- 24 Didymium(Ac)e -------- 4.40 Didyinium - ----------- 2 Y(AC)3 ------------------ 3.70 Y ---- ----------------- 12.5 Yttrium 3,5-di-tert-butyl-4-hydroxybenzo@ate -- 10 Al(OH)(AC)2 ------------ 3. @q6 Al(011) --------------- 11.5 Lanthan um 3,(5-di-tert-butyl - 4 - hydrozybenzoate -------------------------------- 10 'Didyinium is a inixture of neodymium and prageodymium. 55 C erium 3,5-di-tert-butyl-4-hydroxybenzoate -- 91/2 N eodyrnium 3,5-di@tert-butyl - 4 - hydroxybenzoate -------------------------------- 141/2 The metal benzoates were purified, and their identity S amarium 3,5-di - tert - butyl - 4 - hydroxybenestablished by infrared spectroscopy. zoate -------------------------------- 14 60 Gadolini um 3,5- di-tert - butyl - 4 - hydroxy benExample IV zoate ------------------------- ------- 101/2 Dysprosium 3,5-di-tert - butyl - 4 - hydroxybenThe metal salts described in the previous examples zoate --------- ----------------------- 14 were evaluated as thermal- antioxidants in polypropylene. E rbium 3,5-di-tert-butyl-4-hydroxybenzoate -- 91/2 In the heat aging test, polypropylene film samples five mils 65 Didyniium I 3,5-di-tert-butyl - 4 - hydroxybenin thickness were maintained in an oven at 133' C. Each zoate -------------------------------- 14 sample was tested for loss of elongation twice each day Basic aluminum 3,5-di-tert-butyl-4-hydroxyuntil the film tore easily. The number of hours shown in benzoat e ----------------------------- 81/2 the table are the total elapsed hours before the film tested I Didymii7.m is a mixture of neodymiura and praseodymium. lost its tensile strength and flexibility. It wifl be seen from 70 the table that the candidele compounds increased the heat I
