Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/48—Separation; Purification; Stabilisation; Use of additives
  • C07C67/52—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation
  • C07C67/54—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation by distillation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C43/00—Ethers; Compounds having groups, groups or groups
  • C07C43/02—Ethers
  • C07C43/20—Ethers having an ether-oxygen atom bound to a carbon atom of a six-membered aromatic ring
  • C07C43/23—Ethers having an ether-oxygen atom bound to a carbon atom of a six-membered aromatic ring containing hydroxy or O-metal groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/24—Preparation of carboxylic acid esters by reacting carboxylic acids or derivatives thereof with a carbon-to-oxygen ether bond, e.g. acetal, tetrahydrofuran
  • C07C67/26—Preparation of carboxylic acid esters by reacting carboxylic acids or derivatives thereof with a carbon-to-oxygen ether bond, e.g. acetal, tetrahydrofuran with an oxirane ring
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/48—Separation; Purification; Stabilisation; Use of additives
  • C07C67/62—Use of additives, e.g. for stabilisation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C69/00—Esters of carboxylic acids; Esters of carbonic or haloformic acids
  • C07C69/52—Esters of acyclic unsaturated carboxylic acids having the esterified carboxyl group bound to an acyclic carbon atom
  • C07C69/533—Monocarboxylic acid esters having only one carbon-to-carbon double bond
  • C07C69/54—Acrylic acid esters; Methacrylic acid esters
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D211/00—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings
  • C07D211/92—Heterocyclic compounds containing hydrogenated pyridine rings, not condensed with other rings with a hetero atom directly attached to the ring nitrogen atom
  • C07D211/94—Oxygen atom, e.g. piperidine N-oxide
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/13—Phenols; Phenolates
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/34—Heterocyclic compounds having nitrogen in the ring
  • C08K5/3412—Heterocyclic compounds having nitrogen in the ring having one nitrogen atom in the ring
  • C08K5/3432—Six-membered rings
  • C08K5/3435—Piperidines
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K15/00—Anti-oxidant compositions; Compositions inhibiting chemical change
  • C09K15/04—Anti-oxidant compositions; Compositions inhibiting chemical change containing organic compounds
  • C09K15/06—Anti-oxidant compositions; Compositions inhibiting chemical change containing organic compounds containing oxygen
  • C09K15/08—Anti-oxidant compositions; Compositions inhibiting chemical change containing organic compounds containing oxygen containing a phenol or quinone moiety
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K15/00—Anti-oxidant compositions; Compositions inhibiting chemical change
  • C09K15/04—Anti-oxidant compositions; Compositions inhibiting chemical change containing organic compounds
  • C09K15/30—Anti-oxidant compositions; Compositions inhibiting chemical change containing organic compounds containing heterocyclic ring with at least one nitrogen atom as ring member

Definitions

• the present invention relates to a composition stabilized for purification.
• the present invention describes processes for the purification and for the preparation of hydroxyalkyl (meth) acrylates.
• Monomers e.g. Styrene or (meth) acrylates tend during storage to an undesirable, premature polymerization. To prevent the same, therefore, these monomers are usually added polymerization inhibitors.
• a process for the stabilization of (meth) acrylates is the subject of European Patent Application EP-A-0 620 206, for example.
• (meth) acrylates in particular can be stabilized by a mixture of polymerization inhibitors comprising at least one N-oxyl compound, at least one phenol compound and at least one phenothiazine compound.
• reaction mixtures obtained in the preparation of hydroxyalkyl (meth) acrylates are treated with polymerization inhibitors for purification, and the polymerization inhibitors can also be added during the preparation.
• a preferred process for the purification of hydroxyalkyl (meth) acrylates is described inter alia in European Patent Application EP-A-1 090 904. Accordingly, a reaction mixture comprising hydroxyalkyl (meth) acrylates can be particularly efficiently purified by a distillation combined with a thin film evaporator.
• EP-A-1 090 904 Processes lead to relatively pure products at high yields.
• Another object of the invention was to provide a process in which a hydroxyalkyl (meth) acrylate can be obtained very selectively. Furthermore, the method should provide as constant as possible product quality. Further, a stabilized hydroxyalkyl (meth) acrylate composition should be provided which shows substantially no discoloration after a long storage.
• the present invention accordingly provides a composition stabilized for purification with at least one hydroxyalkyl (meth) acrylate, which is characterized in that the composition comprises hydroquinone monomethyl ether and 4-hydroxy-2, 2,6,6-tetramethylpiperidine-N-oxyl.
• hydroxyalkyl (meth) acrylates can be obtained very selectively. Furthermore, the processes provide a very consistent product quality.
• a stabilized hydroxyalkyl (meth) acrylate composition obtainable by the method of the present invention shows substantially no discoloration after a long storage.
• composition stabilized for purification with at least one hydroxyalkyl (meth) acrylate, wherein the term "a composition stabilized for purification” means that the composition may be subjected to purification without causing excessive polymerization.
• a stabilized for a purification composition shows a change in the color number of at most 30, more preferably at most 20 after a storage of 5 hours at 100 0 C.
• the color number can in particular by the in DE-A-10,131 479 (determination of the color according to the platinum-cobalt scale, also called APHA or turbidity number) can be determined, wherein in the document DE-A-10 131 479 filed with the German Patent and Trademark Office on 29.06.2001 with the Applicant's DE 101 31 479.5, set forth methods for determining the platinum-cobalt color number for purposes of disclosure in this application. This procedure was developed on the basis of DIN EN ISO 6271.
• a composition according to the invention comprises
• Hydroxyalkyl (meth) acrylates includes hydroxyalkyl methacrylates, hydroxyalkyl acrylates and mixtures thereof. Hydroxyalkyl (meth) acrylates are well-known in the art esters of (meth) acrylic acid whose alcohol radical has at least one hydroxyl group.
• the preferred hydroxyalkyl (meth) acrylates include, for example, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, especially 2-hydroxypropyl methacrylate and 3-hydroxypropyl methacrylate, and / or hydroxypropyl acrylate, especially 2-hydroxypropyl acrylate and 3-hydroxypropyl acrylate.
• the proportion of hydroxyalkyl (meth) acrylate in a composition according to the invention which is stabilized for purification is preferably at least 75% by weight, particularly preferably at least 95% by weight. This proportion can be determined in particular by gas chromatography.
• composition according to the invention comprises hydroquinone monomethyl ether (CAS number 150-76-5) and 4-hydroxy-2,6,6,6-tetramethylpiperidine-N-oxyl (CAS number 2226-96-2).
• the weight ratio of hydroquinone monomethyl ether to 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl is not critical per se. Surprising advantages can be achieved in particular in that this weight ratio is in the range from 40: 1 to 1:10, preferably in the range from 20: 1 to 1: 2 and very particularly preferably in the range from 10: 1 to 3: 1.
• the proportion of hydroquinone monomethyl ether in the Purification stabilized composition is preferably 25 to 1000 ppm, more preferably 35 to 500 ppm.
• highly stabilized compositions can be obtained which can be stored for a long period of time.
• These compositions are preferably characterized by a proportion of hydroquinone monomethyl ether in the range from 25 ppm to 1000 ppm, in particular 50 to 500 ppm, particularly preferably 100 to 400 ppm and very particularly preferably 150 to 350.
• Particular advantages can also be obtained by lower stabilized compositions, which preferably have a content of hydroquinone monomethyl ether in the range of 35 ppm to 100 ppm, more preferably 40 to 80 ppm.
• 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl is used to stabilize the composition.
• the proportion of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl in the composition stabilized for purification may preferably be 20 to 200 ppm, more preferably 30 to 100 ppm and most preferably 40 to 60 ppm.
• composition which has the smallest possible proportion of N, N'-diphenyl-p-phenylenediamine, ⁇ /, ⁇ / '- di-2-naphthyl-p-phenylenediamine, N, N'-D ⁇ -p-tolyl-p-phenylenediamine, ⁇ / -1, 3-dimethylbutyl- ⁇ / '- phenyl-p-phenylenediamine, ⁇ / -1, 4-dimethylpentyl- ⁇ /' - phenyl-p-phenylenediamine, phenothiazine, Nigrosine Base BA and / or 1, 4-benzoquinone has.
• compositions which are not more than 10 ppm, more preferably not more than 1 ppm, and very particularly preferably no measurable amount of ⁇ /, ⁇ / '- diphenyl-p-phenylenediannine, N, N'-D ⁇ -2-naphthyl-p-phenylenediamine, / V, / V'-di-p-tolyl-p-phenylenediamine, / V-1, 3-dimethylbutyl-A / '- phenyl-p-phenylenediamine, ⁇ / -1, 4-dimethylpentyl- ⁇ /' - phenyl-p-phenylenediamine, phenothiazine, nigrosine base BA and / or 1, 4- Include benzoquinone.
• a composition of the invention that has been stabilized for purification may include other polymerization inhibitors.
• Suitable polymerization inhibitors include for example tocopherol, preferably ⁇ -tocopherol, ⁇ /, ⁇ / -Diethylhydroxylamin, ammonium ⁇ / -nitrosophenylhydroxylamin (Cupferron) and / or hydroquinone.
• Particular improvements can be achieved in particular by a proportion of these polymerization inhibitors in the range from 10 ppm to 80 ppm, more preferably in the range from 20 ppm to 40 ppm.
• compositions characterized by a weight ratio of tocopherol to 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl in the range of preferably 10: 1 to 1:10, particularly preferably in the range of 2: 1 to 1: 4.
• the weight ratio of N, N-diethylhydroxylamine to 4-hydroxy-2,2,6,6-tetramethylpipehdin-N-oxyl is in the range of 10: 1 to 1:10, more preferably in the range of 2: 1 to 1: 4th
• the weight ratio of ammonium ⁇ / -nitrosophenylhydroxylamine (Cupferron) to 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl in the range of 10: 1 to 1:10 may be particularly preferred ranging from 2: 1 to 1: 4.
• compositions in which the weight ratio of hydroquinone to 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl is preferably in the range from 10: 1 to 1:10, particularly preferably in the range from 2: 1 to 1: 4.
• a composition of the invention can be used in particular in a process for the purification of hydroxyalkyl (meth) acrylates, which is also the subject of the present invention.
• oxygen may be used.
• This can be used, for example, in the form of air, wherein the amounts are advantageously metered so that the content in the gas phase above the reaction mixture remains below the explosion limit.
• Air quantities in the range of 0.1 to 10, more preferably 1 to 5 and very particularly preferably 2 to 4 standard liters per hour and kg of the composition stabilized for purification are preferred.
• inert gas-oxygen mixtures e.g. Nitrogen-oxygen or argon-oxygen mixtures can be used.
• a stabilized for purification composition prior to purification which can be effected for example by distillation, are treated with oxygen.
• oxygen for this purpose, in particular air can be passed through the composition to be purified.
• gaseous or volatile constituents can be separated from the composition before it is subjected to a further purification, preferably a distillation.
• a plant is preferably used which comprises a still.
• This surprising advantages can be achieved in particular by a column with a low separation efficiency.
• the yield and energy efficiency of the plant can be improved by this configuration.
• the column used has at most 4, more preferably at most 3 separation stages.
• a column is preferably used with at least 2 separation stages.
• the number of separation stages in the present invention refers to the number of plates in a tray column or the number of theoretical plates in the case of a packed column or a packed column.
• a column can be used which has separation-technically acting internals, which corresponds approximately to a separation stage.
• the supply of the stabilized for a purification composition of the present invention can be made above or below the above-described internals, and, depending on the nature of the same, the composition of the invention can also be initiated within the range of the internals.
• Particular advantages can be achieved, inter alia, by feeding the composition of the present invention into the column above the internals.
• the term "above the internals" means that the heavy-boiling constituents of the introduced composition are passed through the internals before they are removed from the column, which in particular provides advantages in terms of yields and purity of purified composition be carried out particularly efficiently.
• the column of the present invention can be operated with or without column reflux, wherein a particularly high purity can be achieved surprisingly by an embodiment without column reflux.
• the column is preferably operated at a gas loading factor of at most 2 Pa 05 .
• the gas loading factor, wherein the second evaporator is operated is preferably in the range of 0.8 to 1, 8 Pa 0 '. 5
• the gas loading factor (F factor) is calculated from the gas velocity related to the empty cross-section of the pipe for the discharge of the gas multiplied by the root of the gas density.
• the pressure at which the distillation takes place may preferably be in the range of 0.1 to 20 mbar absolute, more preferably in the range of 0.5 to 10 mbar and most preferably 1 to 5 mbar absolute, these figures being based on the top pressure of the column are related.
• a part of the composition obtained from the bottoms of the still can be converted into the gas phase with at least one evaporator, for example a thin-film evaporator or a circulation evaporator, and fed into the still.
• at least one evaporator for example a thin-film evaporator or a circulation evaporator
• a preferred system for carrying out the process for the purification of hydroxyalkyl (meth) acrylates has a thin-film evaporator and / or a circulation evaporator.
• FIG. 1 is a schematic representation of a plant suitable for the purification of hydroxyalkyl (meth) acrylates, without this being intended to limit it.
• the system shown in FIG. 1 can be supplied via a feed line 1 with a composition comprising hydroxyalkyl (meth) acrylates.
• feed line 1 leads into a container 2 in which the composition to be purified is treated with oxygen.
• air can be introduced into container 2 via supply line 3, which is discharged via discharge line 4 from container 2.
• the oxygen-treated composition is transferred from container 2 via line 5 into the distillation column 6, which is presently provided with internals, which preferably correspond in terms of separation technology approximately to a separation stage.
• the supply of the composition is preferably carried out above the internals, as indicated schematically in the drawing.
• the top product is withdrawn via line 7 of the distillation column 6 from the plant, in which a cooler 8 is provided.
• a thin film evaporator 10 To increase the yield of the bottom of the distillation column 6 is introduced via line 9 in a thin film evaporator 10, wherein the gaseous products obtained in the thin film evaporator 10 are fed via line 11 of the distillation column 6.
• the in the thin-film evaporator 10th unevaporated portion of the supplied composition is fed via line 12 to a second distillation column 13, which in the present case is also provided with internals, which preferably correspond in terms of separation technology to approximately one separation stage.
• the supply of the composition is preferably carried out above the internals, as indicated schematically in the drawing.
• the top product obtained from the second still 13 is introduced into the thin-film evaporator 10 via line 14, in which a cooler 15 is provided.
• the sump of the second still 13 is fed via line 16 to a second thin-film evaporator 17.
• the gaseous products obtained are introduced via line 18 into the second distillation column 13.
• the by-products obtained are taken from the system via line 19.
• the composition stabilized for purification may preferably be obtained by a reaction which serves to prepare hydroxyalkyl (meth) acrylates.
• Such processes, which comprise a purification according to the invention, are likewise provided by the present invention.
• the composition set forth above can be obtained by reacting (meth) acrylic acid with at least one epoxide in the presence of a catalyst.
• (meth) acrylic acid in the context of the present invention comprises in particular methacrylic acid, acrylic acid and mixtures thereof.
• an epoxide is used as second starting material.
• the preferred epoxides include in particular ethylene oxide and propylene oxide.
• the molar ratio of (meth) acrylic acid to epoxide may, for example, be in the range from 2: 1 to 1: 2, more preferably in the range from 0.9: 1 to 1: 1, 1.
• catalysts are preferably used.
• Preferred catalysts are disclosed inter alia in EP-A-1 231 204 filed on 31.01.2002 at the European Patent Office with the application number EP 02002363.6, the disclosure of this document, in particular the catalysts and processes described therein for the preparation of hydroxyalkyl (meth) acrylates be incorporated into the present application for purposes of the disclosure.
• the degree of conversion, based on (meth) acrylic acid is preferably at least 95, particularly preferably at least 99 and very particularly preferably at least 99.5 mol .-%.
• the degree of conversion can be adjusted in particular over the reaction time and the reaction temperature.
• the reaction takes place preferably at a temperature in the range of 50 to 100 0 C, particularly preferably in the range of 60 to 80 0 C instead.
• the preparation can be carried out continuously or batchwise.
• the reaction time of batchwise processes is preferably in the range of 2 to 10 hours, more preferably 4 to 8 hours.
• the residence time in continuous processes may preferably be in the range from 1 minute to 60 minutes, more preferably in the range from 2 minutes to 30 minutes.
• the pressure used to prepare the hydroxyalkyl (meth) acrylate is preferably in the range from 0.5 to 25 bar, more preferably in the range from 1 to 3 bar.
• reaction of (meth) acrylic acid with epoxide can be carried out both continuously and batchwise.
• the process for the preparation of Hydroxyalkyl (meth) acrylates can be carried out in bulk, ie without the use of a further solvent. If desired, an inert solvent can also be used.
• polymerization inhibitors set forth above in particular of hydroquinone monomethyl ether and 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl, may be added before or during the reaction of (meth) acrylic acid with an epoxide. Due to the degradation of the polymerization inhibitors during the reaction, however, higher amounts may be added, wherein the proportion of hydroquinone monomethyl ether which is added to the reaction mixture for the reaction of (meth) acrylic acid with epoxides, preferably in the range of 25 to 1000 ppm, particularly preferably 100 to 500 ppm.
• the proportion of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N- oxyl, which is added to the reaction mixture for the preparation of hydroxyalkyl (meth) acrylate from (meth) acrylic acid and epoxides may preferably be in the range from 20 to 200 ppm, more preferably in the range from 30 to 80 ppm.
• the reaction mixture for preparing the hydroxyalkyl (meth) acrylate comprises at most 10 ppm, more preferably at most 5 ppm, and most preferably at most 1 ppm of ⁇ /, ⁇ / '- diphenyl-p-phenylenediamine, ⁇ /, ⁇ /' - di -2-naphthyl-p-phenylenediamine, ⁇ /, ⁇ / '- di-p-tolyl-p-phenylenediamine, ⁇ / -1, 3-dimethylbutyl- ⁇ /' - phenyl-p-phenylenediamine, ⁇ / -1, 4-dimethylpentyl- ⁇ / '- phenyl-p-phenylenediamine, phenothiazine, nigrosine base BA and / or 1, 4-benzoquinone.
• the polymerization inhibitors contained in the composition stabilized for a purification can be added after the reaction, but before the purification.
• hydroxyalkyl (meth) acrylate composition shows previously unknown properties, so that this is also the subject of the present invention.
• the color number of the composition is at most 20, particularly preferably at most 10, measured by the process set forth in DE-A-10 131 479.
• the proportion of hydroxyalkyl (meth) acrylate in a composition according to the invention obtainable by the process set out above is preferably at least 97% by weight, more preferably at least 98% by weight. This proportion can be determined in particular by gas chromatography.
• the hydroxyalkyl (meth) acrylate composition according to the above purification comprises 20 to 80 ppm, more preferably 30 to 50 ppm of hydroquinone monomethyl ether and 0.1 to 2 ppm, more preferably 1 to 2 ppm of 4-hydroxy-2.2.6 , 6-tetramethylpiperidine-N-oxyl.
• the weight ratio of hydroquinone monomethyl ether to 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl in a hydroxyalkyl (meth) acrylate composition obtainable according to the invention is preferably in the range from 100: 1 to 10: 1, more preferably in the range from 40: 1 to 20: 1.
• the hydroxyalkyl (meth) acrylate composition according to the above purification may comprise 1 to 50 ppm, more preferably 5 to 25 ppm tocopherol, preferably ⁇ -tocopherol.
• the tocopherol compounds which can be used in the context of the invention are chroman-6-ols (3,4-dihydro-2H-1-benzopyran-6-ols) substituted in the 2-position by a 4,8,12-thymethyldecyl radical ,
• the tocopherols which can preferably be used according to the invention include alpha-tocopherol, beta-tocopherol, gamma-tocopherol, delta-tocopherol, zeta-tocopherol and eta-tocopherol, all of the abovementioned compounds in each case in the (2R, 4'R, 8'R) - Form, as well as alpha-tocopherol in the (all-rac) form.
• Alpha-tocopherol in the (2R, 4'R, 8'R) form (common name: RRR-alpha-tocopherol) and the synthetic racemic alpha-tocopherol (all-rac-alpha-tocopherol) are preferred. Of these, in turn, the latter is particularly interesting because of the relatively low price.
• a hydroxyalkyl (meth) acrylate composition which is obtainable by a purification according to the invention preferably comprises no N, N'-diphenyl-p-phenylenediamine, ⁇ /, ⁇ / '- di-2-naphthyl-p-phenylenediamine, N, N'-D-p-tolyl-p-phenylenediamine, ⁇ / -1, 3-dimethylbutyl- ⁇ / '- phenyl-p-phenylenediamine, ⁇ / -1, 4-dimethylpentyl- ⁇ /' - phenyl-p- phenylenediamine, phenothiazine, nigrosine base BA and / or 1, 4-benzoquinone.
• a hydroxyalkyl (meth) acrylate composition obtained according to the present invention may preferably be used for the preparation of polymers.
• these compositions show, with the same stabilization, in particular an equal proportion of hydroquinone monomethyl ether, an improvement in the color number which is achieved by the in DE-A-10 131 479 can be determined according to a conventional polymerization, which can be carried out preferably at temperatures less than or equal to 180 0 C, preferably less than or equal to 160 0 C and most preferably less than or equal to 140 ° C. If a color number can be tolerated, which is also achieved with compositions of the prior art, compositions obtainable according to the invention require less stabilization, in particular a lower proportion of hydroquinone monomethyl ether. Lower stabilization can provide additional benefits.
• a composition comprising 2-hydroxyethyl methacrylate (HEMA) was prepared in accordance with the present invention using a stabilizer mixture comprising 200 ppm hydroquinone monomethyl ether and 50 ppm 4-hydroxy-2,6,6,6-tetramethylpiperidine N-oxyl for preparation and purification includes.
• the purification was carried out in a plant explained in more detail in FIG. 1, which comprised two distillation columns and two thin-film evaporators.
• a composition containing about 50 ppm of hydroquinone monomethyl ether and about 1 ppm of hydroxy-2,6,6,6-tetramethylpiperidine N-oxyl was obtained.
• the color number of the prepared composition was less than 5.
• the shelf life of this composition was measured by the determination of the color number, whereby different experiments were carried out. The color number was measured by the method set forth in DE-A-10 131 479. So the shelf life was determined at 30 0 C for 6 months. For this purpose, 25 g of the composition were filled into a 30 ml bottle (brown, wide-necked). The storage was carried out in a convection oven at 30 0 C. After 6 months, the color number was measured.
• the color number was determined after storage at 100 ° C for 5 hours in a short-term test.
• the color number of a standard clearcoat was measured. This was prepared by polymerization of a monomer mixture within 4-6 h at temperatures> 140 0 C under a nitrogen atmosphere. The solids content of the formulation was about 62%, the proportion of HEMA in the copolymer about 30%.
• Example 1 was essentially repeated except that the proportion of hydroquinone monomethyl ether in the composition obtained after purification was increased from 50 ppm to 200 ppm.
• the color number of the prepared composition was less than 5.
• Example 1 was substantially repeated except that an additional 20 ppm of tocopherol was added to the composition obtained after purification.
• the color number of the prepared composition was less than 5.

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