Title of Invention

A MIXTURE AND A PROCESS FOR INHIBITING THE PREMATURE POLYMERIZATION OF VINYL-CONTAINING MONOMERS

Abstract

Mixtures contain (A) vinyl-containing monomers, and (B) an effective amount of a mixture inhibiting the premature polymerization of the vinyl-containing monomers during the purification or distillation and containing (i) from 0.05 to 4.5 % by weight, based on the total mixture (B), of at least one N-oxyl compound of a secondary amine which carries no hydrogen atoms on the a-carbon atoms and (ii)from 99.95 to 95.5 % by weight, based on the total mixture (B), of at least one nitro compound, and a mixture (B) is used for inhibiting the premature polymerization of monomers.

Full Text

The present invention relates to mixtures which, in addition to vinyl-containing monomers for preventing their premature polymerization during purification or distillation, also contain at least one nitroxyl and at least one nitro compound, a process for purifying or distilling such monomers without their premature polymerization taking place, and the use of mixtures which con-bain nitroxyl and nitro compounds for inhibiting the premature polymerization of vinyl-containing monomers. It is known that many unsaturated compounds tend to polymerize, as a rule by free radical polymerization, when the temperatures increase. For example, vinylaromatic compounds, such as styrene or a-methylstyrene, must be stabilized with suitable compounds in order to prevent premature polymerization during distillative purification of the crude products obtained on a large industrial scale. Usually, these stabilizers or polymerization inhibitors are added before the purification step to the crude products to be distilled. In spite of this measure, considerable eimounts of polymers are still obtained. In individual cases, espeC1ally when aperational faults occur, complete polymerization of the monomers or monomer mixtures present may occur during purification or listillation. This results in high costs owing to the very Comdex purification and the loss of production. SSR patents 1,027,150, 1,558,888 and 1,139,722 describe the tabilization of styrene by the use of nitroxyl or bisnitroxyl ompounds. apanese publication Hei 1-165 534 discloses I-piperidyloxy erivatives as polymerization inhibitors for styrene. U.S. patent ,733,326 describes the inhibition of the polymerization of vinyl onomers by using free radical precursor compounds. itro compounds, such as 2-nitro-p-cresol or 2,6-dinitro--cresol, are mentioned as polymerization inhibitors in U.S. atents, 4,086,147, 4,105,506 and 4,252,615. U.S. patents ,132,602 and 4,132,603 disclose the use of halogenated nitro-romatic compounds for inhibiting the polymerization of vinyl-romatics during their distillative working-up. However, all the stated nftro compounds have only a small stabilizing effect and therefore have to be used in relatively high concentrations. If the relatively high toxiC1ty of these nitro- "" compounds is also taken into account, their use constitutes a considerable potential danger for the operating personnel and the environment. The use of inhibitors based on N-nitrosodiphenylamine in combination with dinitrocresol derivatives in the distillation of vinylaromatics under reduced pressure is described in U.S. patents 3,988,212 and 4,341,600. When oxygen is present, polymerization of vinylaromatic compounds on heating can be prevented, according to U.S. patents 4,466,904 and 4,468,343, by using an initiator based on phenothiazine, 4-tert-butylcatechol, 2,6-dinitro-o-cresol or 2,6-dinitro-p-cresol with either phenyl-diamine or 4-tert-butylcatechol. According to EP 240 297, polymerization of vinylaromatics on heating can be suppressed by using hydroxyleunine derivatives and dinitrophenol. However, a disadvantage of these inhibitor systems is the strong dependence of their effiC1ency on the oxygen content, i.e. these additives are likely to have different inhibiting effects under the conditions of the purification or distillation, in accordance with the nonuniform distribution of the residual oxygen in the corresponding unit. However, this makes the controlled use more difficult. U.S. patent 5,254,760 describes mixtures of nitroxyl and nitro compounds for stabilizing vinylaromatic compounds during purification or distillation. The nitroxyl and nitro compounds are used in amounts of from 5 to 95 % by weight and from 95 to 5 % by weight, based on the total amount of the mixture. Since nitroxyl compounds are as a rule very expensive, this stabilizing additive, which must be added continuously in a certain amount to the crude product before working-up, constitutes a cost factor which is not negligible. Furthermore, there is the danger that, when polymerization inhibitors having relatively high contents of nitroxyl compound(s) are used, some of these will be entrained into the pure product and will lead there to inhibition of possibly desirable polymerization. A further disadvantage of these mixtures is their relatively low effiC1ency with regard to delaying the polymerization of monomers. If the feed of the inhibitor/crude monomer mixture into the distillation apparatus is interrupted, for example as a result of an operational fault, not only is there a lack of cooling of the column bottom caused by their continuous introduction but in addition, owing to inadequate stabilization, there is an exothermic polymerization with evolution of heat and an assoC1ated increase in temperature, which in turn accelerates the polymerization. In extreme cases, extensive polymer formation over a prolonged period may thus render a corresponding purifi-cation or distillation unit useless. Liong retardation of the polymerization is therefore an important aspect for the operational use of appropriate inhibitors. [t is an object of the present invention to provide mixtures of inyl-containing monomers which are effective for a suffiC1ently Long time and are economically stabilized to prevent premature polymerization during the purification or distillation and result Ln a very small amount of troublesome inhibitor residues in the ure product. e have found that this object is, achieved and that, surprisingly, all these criteria are fulfilled by mixtures which contain A) vinyl-containing monomers, B) an effective amount of a mixture inhibiting the premature polymerization of the vinyl-containing monomers during their purification or distillation and containing, (i) from 0.05 to 4.5 % by weight, based on the total mixture (B), of at least one N-oxyl compound of a secondary amine which carries no hydrogen atoms on the a-carbon atoms and (ii)from 99.95 to 95.50 % by weight, based on the total mixture (B), of at least one nitro compound. referred mixtures are those which contain from 0.1 to 4.0 % by eight of the component (i) and from 99.9 to 96 % by weight of he component (ii), based in each case on the total mixture (B). referred vinyl-containing monomers (A) are those of the formula la) where: R1,R2,R3 and R^, independently of one another, are each hydrogen, Cx-Ce-alkyl, C2-C6-alkenyl, unsubstituted or substituted aromatic or heteroaromatic radicals or halogen, *ith the proviso that not more than two of these radicals are simultaneously unsubstituted or substituted aromatic or heteroaromatic radicals. The C1-Ce-alkyl radicals include the linear alkyl chains of methyl through ethyl to hexyl as well as the corresponding branched radicals. Furthermore, suitable Ca-Ce-alkenyl radicals are Bthenyl, propenyl, etc. up to hexenyl and the groups which are aranched in the saturated moiety. Exeunples of both unsubstituted ind substituted aromatic or heteroaromatic groups are phenyl, jyridyl, alkylphenyl or alkyIpyridyl, such as methylphenyl, nethylpyridyl, ethylphenyl or ethylpyridyl, alkenylphenyl or ilkenyIpyridyl, such as vinylphenyl or vinyIpyridyl, carboxy-ihenyl or carboxypyridy1, formylphenyl or formylpyridy1, sulfo-jhenyl or sulfopyridyl, hydroxyphenyl or hydroxypyridy1, amino-)henyl or aminopyridyl, nitrophenyl or nitropyridyl, as well as japhthyl or napthyl substituted by alkyl, alkenyl, carboxyl, for-lyl, sulfo, hydroxyl, amino or nitro. The halogen radical usually ised is fluorine or chlorine, and occasionally also bromine. :f, for example, compounds having in each case an aromatic or leteroaromatic radical on the one hand and a C1-Ce-alkyl radical )n the other hand are considered, and if the remaining two rad--cals from R^, R2, R3 and R* are each hydrogen, examples of mono-lers to be added are a-methylstyrene (2-phenyl-prop-l-ene), the ;wo P-methylstyrene isomers (C1s- and trans-1-phenyl-prop-l-ene), i-ethylstyrene (2-phenylbut-l-ene), the two P-ethylstyrene isomers C1s- and trans-1-phenylbut-l-ene) up to a-hexylstyrene (2-pheny-.oct-1-ene) and the two P-hexylstyrene isomers (C1s- and :rans-l-phenyloct-l-ene). limilarly, when pyridyl is used instead of the phenyl radical, ;he compounds 2-pyridyl-prop-l-ene, C1s- and trans-1-pyridyl-»rop-l-ene, 2-pyridylbut-l-ene, C1s- and trans-1-pyridylbut-l-ene up to 2-phenyloct-l-ene and the two isomers C1s-l-pyridyl-oct-1-ene and trans-1-pyridyloct-l-ene are obtained. Also included here are of course the isomers which differ in the position of the pyridine-N-atom relative to the bond linking the vinyl to the pyridyl group. If the phenyl or pyridyl radical is substituted by the abovementioned groups, compounds such as a-methylstyrenesulfonic aC1d (2-sulfophenylprop-l-ene), a-methyl-nitrostyrene (2-nitrophenylprop-l-ene), a-ethyl-styrenesulfonic aC1d (2-sulfophenylbut-l-ene), a-ethyl-nitrostyrene (2-nitro-phenylbut-1-ene), the analogous pyridyl monomers or the C1s/trans-isomers of the corresponding ^-substituted compounds are obtained. Here too, the isomers which arise from the position of the substituent on the benzene ring relative to the phenyl-vinyl bond or, in the case of the substituted pyridene radical, from the relative position of the pyridine N-atom, substituent and py-ridyl-vinyl bond to each other are of course included. By choosing an aromatic or heteroaromatic radical on the one hand and a C2-C6-alkenyl group on the other hand, and if the two remaining radicals are once again hydrogen, substituted butadienes are also among the monomers which can be obtained. It is possible to use, for example, the compounds 1- or 2-phenylbuta-diene, 1- or 2-pyridylbutadiene with the corresponding C1s/trans-isomers on the one hand and, in the case of the pyridyl radical, once again the positional isomers arising from the relative position of the N atom to the pyridyl-vinyl bond. Here too, various substituents mentioned further above may occur on the aromatic or tieteroaro-matic system. According to the invention, aromatically or heteroaromatically substituted ethylenes, such as styrene, vinylpyridine, divinyl-aenzene, nitrostyrene, styrolsulfonic aC1ds, vinyltoluene and, if iesired, isomers thereof may also be used. According to the formula (la), three of the radicals Ri, R2, R3, \^ are hydrogen and only one is an aromatic or heteroaromatic ansubstituted or substituted group in these monosubstituted ethylenes, i.e. in the order of phenyl, pyridyl, vinylphenyl, nitro-phenyl, sulfophenyl and methylphenyl. If desired, disubstituted 2thylenes in which two or four radicals Ri, R2, R3, R4 are hydrogen and the remaining radicals are aromatic or heteroaromatic jroups may also be used. Usually, these are symmetrically substituted stilbenes such as 4,4"-diC1minostilbene, 4,4"-dinitrostil-aene, 4,4"-dinitrostilbene-2,2"-disulfonic aC1d, 4,4"-dieimino-3tilbene-2,2"- disulfonic aC1d (flavonic aC1d) or their C1s- or trans-isomers. It is of course also possible to use those isomers which differ from one another with respect to the position of the substituent or of the substituents in the aromatic of heteroaro-matic system relative to the vinyl group. According to the formula (I), in these stilbenes two of the radicals Ri, R2, R3, R4 are hydrogen and the remaining radicals are nonviC1nal radicals, which in this case are also identical, in the order aminophenyl, nitrophenyl, nitrosulfophenyl and aminosulfophenyl. Halogen-containing monomers, such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinyl bromide and chloroprene {2-chloro-1,3-butadiene) may also be used in the claimed mixtures. It is of course possible to use the vinyl-containing monomers not only as. a mixture with their isomers but also as a mixture with one another, as obtained in the crude product, for exeimple in their preparation. Further preferred vinyl-containing monomers (A) are those of the formula (lb) Z2 is hydrogen or C1-C4-alkyl or, together with Z^ , is a saturated or unsaturated C3-, C4- or Cg-alkylene bridge in which one or two CH2 groups may be replaced by NH, N(C1-C4-alkyl), N(C6-C1o-aryl) or oxygen and one or two CH groups may be replaced by N and Z3 is hydrogen, C1-C4-alkyl or a radical which, together with Z^, is a saturated or unsaturated C3-, C4- or Cs-alkylene bridge in which one or two CH2 groups may be replaced by NH, N(C1-C4-alkyl), N(C6-C1o-aryl) or oxygen and one or two CH groups may be replaced by N. The monomers (A) of the formula (lb) which are contained in the novel mixtures may contain oxygen as Q. Among these monomers, th vinyl ethers in which Z^ is C1-C4-alkyl, i.e. methyl, ethyl, " ,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl, are particularly suitable as a component of the novel monomer compositions. If Q is -NZ2-, zi is preferably -C0-z3. Other suitable radicals Z^ in addition to hydrogen and the stated C1-C4-alkyl groups are those radicals, which, together with -NZ2-, form a saturated or unsaturated 5- to 7-membered ring. Examples of such ring systems are: in particular the N-pyrrolidinonyl and the N-caprolactamyl radicals. Preferred monomers in the novel compositions are N-vinylform-amide, N-vinyl-2-pyrrolidone, N-vinyl-e-caprolactam and the above-mentioned C1-C4-alkyl vinyl ethers. N-vinylformamide is particularly preferred among these monomers. Preferred N-oxyl compounds in the novel monomer compositions are those of the general formula (II) where R5 and R^, independently of one another, are each C1-C4-alkyl, or phenyl or, together with the carbon atom to which they are bonded, are a 5- or 6-membered saturated hydrocarbon ring. is hydrogen, hydroxyl, amino or an m-valent organic radical bonded via oxygen or nitrogen or, together with R^ is oxygen or a ring structure defined under R^, is hydrogen, C1-C12-alkyl or, together with R"", is oxyg« or, together with R" and the carbon atom to which they are bonded, forms the following ring structures where, when R" together with R8 forms a common radical, m is 1, I R9 is hydrogen, C1-C12-alkyl or -(CH2)z-COORio, R1° are identical or different C1-C1s-alkyl radicals, k is 0 or 1, 2 and p, independently of one another, are each from 1 to 12 and m is from 1 to 100. R5 and R^ may be C1-C4-alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl or together may form a tetra- or pentamethylene group. R^ and R^ are each preferably methyl. Examples of suitable radicals R^ are hydrogen, the abovementioned C1-C4-alkyl groups and pentyl, sec-pentyl, tert-pentyl, neopentyl, hexyl, 2-methylpentyl, heptyl, 2-methylhexyl, octyl, isooctyl, 2-ethylhexyl, nonyl, 2-methylnonyl, isononyl, 2-methyloctyl, decyl, isodecyl, undecyl, isoundecyl, dodecyl and isododecyl, (the names isooctyl, isononyl and isodecyl are trivial names and originate from the carbonyl compounds obtained by the oxo synthesis; cf. Ullmann"s Encyclopedia of Industrial Chemistry, 5th Edition, Vol. Al, Pages 290-293, and Vol. AlO, Pages 284 and 285). p is preferably from 6 to 12, particularly preferably 9. z is preferably from 1 to 4, particularly preferably 2. Examples of suitable radicals R^ in addition to hydrogen are the abovementioned C1-C12-alkyl groups. R^ is preferably hydrogen, C1-C4-alkyl or (CH2)z-COO(C1-C6-alkyl), particularly preferably -CH2-CH2-COO(CH2)ii-CH3 and -CH2-CH2-COO(CH2 )i3-CH3. Rio may be, for example, one of the abovementioned C1-C12~alkyl groups or tridecyl, isotridecyl, tetradecyl, pentadecyl, hexa-decyl, heptadecyl or octadecyl. Dodecyl and hexadecyl are preferred . Preferred monovalent organic radicals R^ bonded via oxygen are hydroxy! and (C1-C4)-alkoxy groups, for example methoxy, ethoxy, propoxy or tert-butoxy. Preferred m-valent radicals R"^ are, for example, the following radicals where Rli is C1-C12-alkyl or -(CH2)2-COORl0, Ri2 is hydrogen or C1-C1g-alkyl, R13 is C1-C18-alkyl, vinyl or isopropenyl, Ri4 is C8-C22-alkyl, Ri5 is hydrogen or an organic radical as usually formed in the free radical polymerization of the starting monomers, k is . 0 or 1, X is from 1 to 12 and n is an even number m. If R" is one of these radicals, R^ is preferably hydrogen, m may be from 1 to 100. m is preferably 1,2,3,4 or a number from 10 to 50, mixtures generally being used espeC1ally in the case of the oligomeric or polymeric radicals R^ . Suitable radicals R^^ are the same radicals as stated for R^. R^^ is preferably C1-C4-alkyl. Suitable radicals R^^ in addition to hydrogen are the same radicals as have been stated for R^o. Ri2 is preferably hydrogen. Suitable radicals R^^ are vinyl, isopropenyl and Cjs-C1y-alkyl. Examples of suitable radicals Ri^ are the abovementioned Z8-Cx8~alkyl radicals and nonadecyl, eicosyl, uneicosyl and loeicosyl. Mixtures of different radicals R^*, which differ in the Length of the carbon chain are preferred. RIS is hydrogen or an organic radical as formed in the free radical polymerization of the starting monomers, for example a radical which is formed from the polymerization initiator or from a radical occurring as an intermediate, or another such radical as Is familiar to a person skilled in the art. ■r ^^0 Preferred nitroxyl compounds as component (i) of the novel monomer compositions are also the following: 1-oxy1-2,2,6,e-tetramethylpiperidine, l-oxyl-2,2,6,6-tetramethylpiperidin-4-ol, l-oxyl-2,2,6,6-tetramethylpiperidin-4-one, l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl acetate, l-oxyl-2,2,6,6-tetrainethylpiperidin-4-yl 2-ethylhexanoate, l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl stearate, l-oxyl-2,2,6,6-tetreunethylpiperidin-4-yl benzoate, l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl (4-tert-butyl)benzoate, bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sucC1nate, bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipate, bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) sebacate, bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) n-butylmalonate, bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) phthalate, bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) isophthalate, bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) hexahydroterephtha-late, N,N"-bis(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)adipinamide, N-(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)caprolactam, N-(l-oxyl-2,2,6,6-tetreunethylpiperidin-4-yl)dodecylsucC1nimide, 2,4,6-tris-[N-butyl-N-(l-oxyl-2,2,6,6-tetramethylpiperi-din-4-yl]-s-triazine, 4,4"-ethylenebis(l-oxyl-2,2,6,6-tetramethylpiperazin-3-one), N,N"-bis (l-oxyl-2,2,6,6-tetr5imethylpiperidin-4-yl)-N,N"-bis-f or-myl-l,6-diaminohexane and tris-(2,2,6,6-tetramethyl-l-oxylpiperidin-4-yl) phosphite. The nitroxyl compounds described can be prepared from the corresponding piperidine compounds by oxidation, for example with hydrogen peroxide. Details of this oxidation are stated, for example, in the prior German patent application 195 101 84.7. The secondary eimines which carry no hydrogen atoms on the a-carbon atoms, such as piperidine compounds, and their preparation are generally known. Since the oxidation reactions do not always go to completion, the piperidine compounds serving as starting compound and partially oxidized intermediates may also be present in the novel monomer compositions. Monomer inxxT:ures conxiain/ as componeiii. (j.x;/ eii. xesasT. une axo- matic nitro compound of the formula (III) ~--- rhere :ifi,Ri"^,Ris and R^", independently of one another, are each hydrogen, C1-Ce-alkyl, halogen or a radical of the formula CN, SCN, NCO, OH, NO2, COOH, CHO, SO2H or SO3H, ith the proviso that at least one of the radicals R^^, R^"^, R^^ nd Ri^ is nitro, and the aromatic ring may additionally be benzo-used. xamples of suitable compounds are 1,3-dinitrobenzene, 1,4-dini-robenzene, 2,6-dinitro-4-methylphenol, 2-nitro-4-methylphenol, ,4,6-trinitrophenol, 2,4-dinitro-l-naphthol, 2,4-dinitro-6-ethylphenol, 2,4-dinitrochlorobenzene, 2,4-dinitrophenol, ,4-dinitro-6-sec-butylphenol, 4-cyano-2-nitrophenol and -iodo-4-cyano-5-nitrophenol. Aromatic nitro compounds, such as ,6-dinitro-4-methylphenol, 2-nitro-4-methylphenol, 2,4-dini-ro-6-sec-butylphenol or 2,4-dinitro-6-methylphenol, in which one f the radicals R^^, Ri^, R18 and R^^ is nitro, one is hydroxyl and ne is C1-Cg-alkyl, are preferably used. urthermore, one or more costabilizers selected from the group onsisting of the aromatic nitroso compounds, phenothiazines, uinones, hydroguinones and their ethers, phenols and their thers, hydroxylcunines and phenylenediamines may be added to the ixture (B) in addition to the components (i) and (ii). xamples of suitable aromatic nitroso compounds are p-nitroso-henol, p-nitroso-o-cresol and p-nitroso-N,N"-diethylaniline. iirther costabilizers may also be substituted phenols or hydro-lainones, for example the following: -tert-butyIpyrocatechol, methoxyhydroquinone, 2,6-di-tert-iityl-4-methylphenol, n-octadecyl J3- (3,5-di-tert-butyl-4-hydroxy-tienyl) -propionate, 1,1,3-tris- (2-methyl-4-hydroxy-5-tert-butyl-tienyl) butane, l,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-Jtyl-4-hydroxybenzyl )-benzene, 1,3,5-tris-(3,5-di-tert- butyl-4-hydroxyben2yl) isocyanurate, 1,3,5-tris-[ 13-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl] isocyanurate, 1,3,5-tris-(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate and pentaerythrityl tetrakis-[J3-(3,5-di-tert-butyl-4-hydroxy-phenyl)-propionate]. For stabilization of the novel monomer compositions, these compositions contain an effective amount of the mixture (B), which in general means from 0.0002 to 5, preferably from 0.0005 to 0.5, % by weight, based in each case on the total amount of the monomer composition, of the mixture (B). The mixtures (B) can of course also contain mixtures of different novel nitroxyl and nitroso compounds and of the stated costabil-izers.. fixture (B) can be added to the monomers before or during the purification or distillation in an effective amount, in order to suppress premature polymerization. In speC1fic cases, it may also De necessary to add the components (i) and (ii), with or without :he addition of one or more of the stated costabilizers, separ-itely and then preferably at different points in space. ["he novel stabilizer mixtures (B) may be used either as such or is a suspension or solution with the aid of suitable diluents. ?hey can be used generally for inhibiting premature polymeriz-ition of, preferably, monomers capable of free radical polymeriz-ition and display their stabilizing effect in a broad temperature •ange. They are effective at any conventional storage temperature :rom -50 to +50°C and also at elevated temperature as used, for ixample in the distillation or purification of the monomers. The iressure range of the stabilization process is also not critical, "he stabilizers are effective at atmospheric pressure and also at educed pressure, as used in some distillation processes. Preparation of 600 ml of a 30% strength by weight aqueous solution of hydrogen peroxide (19.6 mol) were added to a suspension of 540 g (1.37 mol) of N,N"-bis-[2,2,6,6-tetramethyIpiper-idin-4-yl]-N,N"-bis-formyl-l,6-diaminohexene, 800 ml of water, 150 ml of isobutanol and 200 mg of magnesium sulfate at 70°C in the course of 2 hours and the mixture was kept at this temperature for a further 16 hours. Thereafter, the mixture was cooled to room temperature and the preC1pitated product was isolated in the usual manner. Yield: 85 %, melting point: from 169 to 170oc. Characterizations show that the product obtained and used for further experiments (referred to below as F) contains about 60 % of the dinitroxyl compound of the above formula. Mixtures: Steady-state measurements: 500 g of the mixtures stated in Table 1 below and comprising styrene, the product F and the nitro compound 2,4-dinitro-6-sec-butylphenol (DNBP) were heated to 110°C under nitrogen at atmospheric pressure in a reaction vessel. 250 g per hour of an identical mixture were metered continuously into this thermostated mixture, and the scune amount was continuously removed. The equilibrium polymer content was measured in the steady state in the discharge. After 360 minutes, a power failure was simulated (batch operation). The metering of the inhibitor was stopped. The temperature was increased continuously to 145°C in the course of 60 minutes. The polymer content was measured at intervals of 30 minutes. The following results were obtained. Nonsteady-state measurements: In a 250 ml round-bottomed flask equipped with a stirrer, reflux condenser and an internal thermometer, the mixtures stated in Table 2 were heated to 140°C under a nitrogen atmosphere by means of an oil bath and were kept at this temperature. On reaching the final temperature of 140°C, the polymer content was determined at intervals of 15 minutes (to = 0 min is the time when the final temperature was reached). The results are shown in Table 2. We claim:- 1. A mixture containing (A) vinyl-containing monomers, (B) an effective amount of a mixture inhibiting the premature polymerization of the vinyl-containing mbnomers during their purification or distillation and containing, (i) from 0.05 to 4.5 % by weight, based on the total mixture (B), of at least one N-oxyl compound of a secondary amine which carries no hydrogen atoms on the a-carbon atoms and (ii)from 99.95 to 95.5 % by weight, based on the total mixture (B), of at least one nitro compound. 2. The mixture as claimed in claim 1, containing from 0.1 to 4.0 % by weight of component (i) and from 99.9 to 96.0 % by weight of component (ii), based in each case on the total mixture (B). J. Ilhe mixture as claimed in claim 1 or 2, which contains, as vinyl-containing monomers (A), compounds of the formula (la) where: R1,R2,R3 and R4, independently of one another, are each hydrogen, C1-C6-alkyl, C2-C6-alkenyl, unsubstituted or substituted aromatic or heteroaromatic radicals or halogen, with the proviso that not more than two or these radicals are simultaneously unsubstituted or substituted aromatic or heteroaromatic radicals. 4. The mixture as claimed in claim 1 or 2, which contains, as vinyl-containing monomers (A), compounds of the formula (lb) Z2 - is hydrogen, or C1-C4-alkyl or, together with Z^ , is a saturated or unsaturated C3-, C4- or Cs-alkylene bridge in which one or two CH2 groups may be replaced by NH, N(C1-C4-alkyl), N(C6-Cio-aryl) or oxygen and one or two CH groups may be replaced by N and Z3 is hydrogen, C1-C4-alkyl or a radical, which, together with Z2, is a saturated or unsaturated C3-, C4- or Cs-alkylene bridge in which one or two CH2 groups may be replaced by NH, N(C1-C4-alkyl), N(C6-Cio-aryl) or oxygen and one or two CH groups may be replaced by N. The mixture as claimed in any of claims 1 to 4, which contains, as component (I), at least one compound of the formula (II) wherein R5 and R^, independently of one another, are each Cx-C4-alkyl or phenyl or, together with the carbon atom to which they are bonded, are a 5- or 6~membered saturated hydrocarbon ring. R7 is hydrogen, hydroxyl, amino or an m-valent organic radical bonded via oxygen or nitrogen or, together with R^ , is oxygen or a ring structure defined under R^ , R8 is hydrogen or C1-C12-alkyl, or together with R^ is oxygen or, together with R" and the carbon atom to which they are bonded, forms the following ring structures where, when R" together with R^ forms a common radical, m is 1, R9 is hydrogen, C1-C12-alkyl or -(CH2)z-COORl0, Rio are identical or different C1-C18-alkyl radicals, k is 0 or 1, z and p, independently of one another, are each from 1 to 12 and m is from 1 to 100. h£ mixture as claimed in claim 5, wherein R"^ in the formula (II) is a radical of the formula wherein Rii is C1-C12-alkyl or -(CH2)z-COOR10, Ri2 is hydrogen or C1-C18-alkyl, R13 is C1-C18-alkyl, vinyl or isopropenyl, Ri4 is C8-C22-alkyl, R15 is hydrogen or an organic radical as usually formed in the free radical polymerization of the starting monomers (A), k is 0 or 1, X is from 1 to 12 and n is an even number m. The mixture as claimed in any of claims 1 to 6, which contains, as jqomponent (ii), at least one aromatic nitro compound of the formula (III) wherein R16,R17,R18 and R19, independently of one another, are each hydrogen, C1-C6-alkyl, halogen or a radical of the formula CN, SCN, NCO, OH, NO2, COOH, CHO, SO2H or SO3H, with the proviso that at least one of the radicals R16, R17, R18 and R19 is nitro and the aromatic ring may additionally be benzofused. 8. The mixture as claimed in claim 1, which contains at least one aromatic nitro compound of the formula (III), with the proviso that at least one of the radicals R16, R17, R18 and R19 is nitro, one is hydroxyl and one is C1-C6-alkyl. 9. The mixture (B) as claimed in any of claims 1, 2, 5 to 8, which also contains one or more costabilizers selected from the group consisting of the aromatic nitroso compounds, phenothiazines, quinones, hydroquinones and their ethers, phenols and their ethers, hydroxylamines and phenylenediamines, in addition to the components (i) and (ii). 10. A process for inhibiting the premature polymerization of vinyl-containing monomers during their purification or distillation, wherein an effective amount of a mixture (B) as claimed in any of claims 1, 2, 5 to 9 is added to the monomers before or during the purification or distillation. 11. A process for inhibiting the premature polymerization of vinyl-containing monomers during their purification or distillation, wherein the components of the mixture (B) as claimed in any of claims 1, 2, 5 to 9 are added individually, each in an effective amount, to the monomers before the purification or distillation. 12. The process as claimed in claim 11, wherein the components are added at different points in space. 13. A mixture substantially as herein described and exemplified. 14. A process for inhibiting the premature polymerization of vinyl-containing monomers substantially as herein described and exemplified.

Documents:

1159-mas-1997 abstract duplicate.pdf

1159-mas-1997 abstract.pdf

1159-mas-1997 claims duplicate.pdf

1159-mas-1997 claims.pdf

1159-mas-1997 correspondence others.pdf

1159-mas-1997 correspondence po.pdf

1159-mas-1997 description (complete) duplicate.pdf

1159-mas-1997 description (complete).pdf

1159-mas-1997 form-19.pdf

1159-mas-1997 form-2.pdf

1159-mas-1997 form-26.pdf

1159-mas-1997 form-4.pdf

1159-mas-1997 form-6.pdf

1159-mas-1997 others-1.pdf

1159-mas-1997 others.pdf

1159-mas-1997 petition.pdf