Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF POLY ALKYL (METH) ACRYLATES

Abstract

An improved process for the preparation of poly alkyl (meth)acrylate: This invention provides to an improved process for the preparation of poly alkyl (meth)acrylates. More particularly the present invention relates to an improved process for production of poly alkyl (meth)acrylates of predetermined molecular weights using a novel initiator system, consisting of stabilized anionic initiators complexed with polydentate bislithium alkoxide. The process could be carried out at temperatures like -20°C and 0°C.

Full Text

This invention relates to an improved process for the preparation of poly alkyl (meth)acrylates. More particularly the present invention relates to an improved process for production of poly alkyl (mcth)acrylatcs of predetermined molecular weights with narrow molecular weight distribution using a novel initiator system, consisting of stabilized anionic initiators complexed with polydentate bislithium alkoxide. The process could be carried out at relatively higher temperatures like -20 °C and 0 °C. A precise control of molecular parameters of alkyl (meth)acrylate polymers using living anionic polymerization technique is considered very important as acrylic polymers, copolymers and functionalizcd polymers find wide variety of applications. However, the living anionic polymerization of alkyl mcthacrylates is possible only under selected experimental conditions (Makromol. Chem., 172, 137, 1973; Polymer J., 4, 271, 1973; J. Polym. Sci. Poly, Chem., 12, 2295, 1974). The problems associated with the living anionic polymerization of alkyl (meth)acrylates arc the presence of secondary reactions involving initiator anion or propagating ester enolate anion with polar ester functional group of monomer and polymer chain. Anionic polymerization of alkly (meth)acrylates proceeds with insignificant side reactions only under judiciously selected experimental conditions. The existence of ester enolate anion in an aggregated form also poses a problem in controlling living anionic polymerization of alkyl (meth)acrylatcs (Makromol. Chem., 181, 149, 1980). It is also known that the equilibrium dynamics of different aggregated state of the ion pairs in alkyl (mcth)acrylate polymerization is the controlling factor in determining the molecular weight distribution (MWD) (Makromol. Chem., 194, 625, 1993). It is observed that a slow exchange between aggregated and non- aggregated ion pairs leads to a broad MWD. Hence the controlling side reactions as well as equilibrium dynamics of cnaloatc ion pairs is necessary to obtain living anionic polymerization of alkyl (meth)acrylate. The optimum conditions for anionic polymerization of alkyl (mcth)acrylates are the use of sterically hindered initiators to prevent side reactions with a carbonyl group of monomer (Macromolecules, 14, 1599, 1981), polar solvent to have a less aggregation as well as faster exchange between different kinds of aggregated ion-pairs, and low temperatures ( Recently, several new methodologies have been reported for the controlled polymerization of alkyl (meth)acrylic esters. Group transfer polymerization (GTP) developed by Du Pont scientists provides an unique method to synthesize poly (alkyl methacrylate)s with controlled molecular weight and narrow molecular weight distributions at ambient temperatures using silyl ketene acetal as initiator in presence of a nucleophilic/Lewis acid catalyst (US patent, 4,417,034, 19S3 and 4,414,372, 1983). However, synthesis of well-defined high molecular weight acrylic polymers with non-polar monomers is not possible by GTP. Highly stabilized anionic initiators bearing tetra-n-butyl ammonium cations have been claimed as good initiating systems for alkyl (meth)acrylales at 25 °C and above (Angew. Chcm. Int. Ed. Engl., 27, 1373, 19SS and US patent 5,194,537, 1993). Recent studies in our laboratory, on MMA polymerization using tctrn-n-butylammonium, teleralkylguanidinium salts of fluorenyl, 9-ethylfluorenyl and 1,1-diphcnylhexyl as initiators show that the large fraction of the initiators docs not take part in the polymerization and polymers with broad molecular weight distributions were obtained. However, recently, Zagala and Hogen-Esch have reported a living polymerization of MMA using tetruphcnylphosphonium triphenylmethanide as initiator in THF at ambient tenuvratures (Mucromolcculcs, 29, 3038,1996 and 30, 18(59, 1997). In order to circuinvcnl the side reactions as well as to influence the dynamics of a^renation equilibrium, various kinds of ligands such as crown ethers or other chelatinc agents (Macromolecules, 28, 7315, 1995; 25, 4457, 1992; and Macromol. Symp., 27, 107, 1996). cryptands (Makromol. Chem, Rapid Commun. 3, 121, 1982), aluminum alkyls (Makromol. Chem. Suppl, 15, 167, 1989; Macromolecules, 25, 5907, 1992) and alkali salts of alkoxidc (Macromol. Chem., 191, 1657, 1990), halides (US patent 4,767,824, 1988; Luxemborg patent 85627, 1984), perchlorates (Macromolecules, 30, 1550, 1997), and alkoxyalkoxides (French patent 9,109,172, 1991 and 9,401,767, 1994) were used in the anionic polymerization of alky! (rnclh)acrylate in conjunction with anionic initiator. Of these, monolithium alkoxyalkoxide additives provide belter control of the polymerization of acrylatc as well as methncryh'.e at low temperature in THF and toluene. Miiller et al showed that the rate of the MMA polymerization in the presence of lithium alkoxyalkoxide additive is extremely high (kp > 1041. mol"1 s"1) in toluene (Polym. Prcpr., Am. Chem. Soc, Div. Polym. Chem, 38, 467, 1997). It would be very difficult to control such a reaction in a batch polymerization-reactor at relatively higher temperature than at -78 °C as the mixing of reagents within the half-life of the polymerization is not possible by conventional methods. Hence, the anionic polymerization of alkyl (mcth)acrylates in the presence of polydenlate monolithium alkoxides is only done _at~7.3.0C. The main object of the present invention is therefore to provide an improved process for the preparation of poly alkyl (mclh)acrylalc in the presence offbislithium salt of glyeols using an anionic initiator in THF or a suitable mixture of THF and an aromatic solvent. Another objective is to enable the polymerization to be conducted in temperature range -78°C to +35°C with adequate control on polymerization. Yet another objective is to enable the production of polymers with a wide range of molecular weight by mere control of initiator concentration in the presence of excess bislithium salt of glycols. Still another objective is to enable the production of block/statistical copolymers using two or three different alkyl (meth)acrylate monomers. As another objective is to produce polymers/copolymers with narrow molecular weight distribution with polydispersities in the range of 1.10 to 1.29 at temperature > -20°C. Accordingly the present invention provides an improved process for the preparation of poly alkyl (meth)acrylate which comprises preparing an organolithium initiator - additive complex of general formula (I), as shown in the drawing accompanying the specification, where RI = linear or branched alkyl group having one to six carbon atoms, R2 = phenyl or alkyl group having one to six carbon atoms, R3 = phenyl or an ester group, R4 = alkyl group having two to three carbon atoms and n = 1 to 4 and IvT is an alkali or alkaline earth metal and M is a lithium atom, in a solvent such as herein described, wherein organolithium initiator and additive is in the range of 1 : 1 to 1 : 40, reacting the obtained organolithium initiator - additive complex with alkyl (meth) acrylate for anionic polymerization, in presence of an organic solvent such as herein described, at temperature ranging -20°C to 0°C to obtain the polymer of alkyl (meth)acrylate, recovering the polymer using non-solvent by conventional precipitation method such as herein described to get the desired poly alkyl (meth) acrylate. In another embodiment, the solvent used for preparing solution of initiator and additive may be such as pure tetrahydrofuran (THF), tetrahydropyran (THP) or a mixture of THF and an aromatic hydrocarbon. In yet another embodiment, the alkyl (meth)acrylates may be such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, lauryl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate and t-butyl acrylate. In still another embodiment, the mole ratio of organolithium initiator to additive can vary from 1:1 to 1:40 preferrably 1:10. In still another embodiment, the concentration of organolithium initiator may be between 0.3 to 2 millimole/liter and the concentration of alkyl (meth)acrylate is in the range of 0.1 to 0.4 mole/liter. In a feature of the present invention, by suitable choice of the monomer to initiator ratio, polymers with predetermined molecular weight can be produced using this novel initiator system. A linear dependence of monomer conversion with time and number average molecular weight (Mn) with conversion is observed. A linear increase of the number average molecular weight determined by the gel permeation chromatography (hereinafter referred to as GPC), Mn.ci'C of PMMAs upon incremental addition of monomer has also been observed at -20 °C and -78 °C. A plot of Mn,Gi>c vs conversion, figure 1 in the drawing accompanying the specification, shows a straight line which is very close to the theoretically calculated, M,,,CAI. from the feed ratios of monomer to initiator for the polymeriztion carried out at -20 °C. An efficient chain extension reaction confirms that the polymerization is free of secondary side reactions such as termination, transfer, and intramolecular backbiting reactions and exhibits characteristic of a living polymerization. The process of the present invention is further described by examples, hereunder which are illustrative only and should not be construed to limit the scope of the invention, in any manner. Example 1 Polymerization of methyl methacrylate in tetrahydrofuran using 1,1-diphenylhexyllithium (DPHLi)-bislithium salt of triethylene glycol initiator system at 0 °C Into a dry 250 mL round bottom flask equipped with magnetic needle, nitrogen/vacuum three-way adapter with rubber septum, was added 100 mL dry tctrahydrofuran. A tctrahydrofuran solution of 1,1-diphenylhexyllithium (DPHLi, -0.08M) was added drop wise under stirring until the initiator color persisted. One millilitre of -0.08M of initiator solution was required to get a persistent color. Then, 1 mL of 0.12 M DPHLi in tetrahydrofuran (1.2 x 10"4 mol) solution was added and the reaction flask was cooled to 0 °C using ice bath. A tetrahydrofuran solution (5.3 mL) containing 1.2 xlO"3 mole of bislithium salt of triethylene glycol was added into the above initiator solution. After few minutes, 2.5 ml of purified methyl methacrylate (freshly distilled from greenish yellow color tri-ethylaluminium-methyl methacrylate complex) was transferred by stainless steel capillary under stirring using pure nitrogen presure and the polymerization was performed at 0 °C for 15 min. The reaction was terminated by adding degassed methanol. The polymer was recovered by precipitation into 400 mL of n-hcxanc. The crude polymer was dried at 40 °C for four hours under vacuum giving 2.35 gm of poly (methyl methacrylate) (100% conversion). Gel permeation chromatography equipped with 100 A, 500 A, 10" A, 10 A and one linear u.-ultrastyragel columns showed that the polymer had M,,,GI>O = 19,200 g/mol and M»/Mn = 1.29. Mn,cai was 19,500 g/mol. Example 2 Polymerization of methyl methactylatc in tetrahydrofuran using 1,1-diphcnylhexyllithium (DPHLi)-bislithium salt of triethylene glycol initiator system at -20 °C Into a flame dried 250 mL round bottom flask equipped with magnetic needle, nitrogeaVacuum three-way adapter with rubber septum, was added 89 mL dry tetrahydrofuran. A tetrahydrofuran solution of 1,1-diphenylhexyllithium (DPHLi, ~O.OSM) was added drop wise under stirring until the initiator color persisted. 1.2 mL of -0.08M of initiator solution was required to get a persistent color. Then, 1.0 x 10"4 mol of DPHLi in THF solution was added and the reaction flask was cooled to -20 °C. A tetrahydrofuran solution (5.3 mL) containingl.O xlO"3 n:ole of bislithium salt of triethylene glycol was added into the above initiator solution. After few minutes, 2 ml of purified methyl methacrylate (freshly distilled from greenish yellow color tri- ethylaluminiurn-methyl methacrylate complex) was transferred by stainless steel capillary under stirring using pure nitrogen presure and the polymerization was performed at -20 °C for 15 min. The reaction was terminated by adding degassed methanol. The polymer was recovered by precipitation into 400 rnL of n-hexane. The crude polymer was dried at 40 °C for four hours under vacuum giving 1.86 gm of poly (methyl methacrylate) (100% conversion). Gel permeation chromatography equipped with 100 A, 500 A, 103 A, 104 A and one linear (i- ultrastyragel columns showed that the polymer had Mn,Gpc = 20,300 g/mol and Mw/Mn = 1.18. Example 3 Polymerization of methyl methacrylate in tetrahydrofuran using 1,1-diphenylhexyllithium (DPHLi)-bislithium salt of triethylene glycol initiator system at -40 °C Into a flame dried 250 mL round bottom flask equipped with magnctie needle, nitrogen/vacuum three-way adapter with nihber septum, was added 70 mL dry tctrahydrofuran. A tctrahydiuuinw solution ofl,l-dipheuylhexyllithiuni (DPHLi, ~O.OSM) was added drop wise under stirring until the initiator color persisted. Then, 1 ml of THF solution containing O.S x 10"4 mol of DPHLi was added and the reaction flask was cooled to -40 °C. A tctrahydrofuran solution (9 mL) containing O.S xlO"3 mole of bislithium salt of triethylene glycol was added into the above initiator solution. After few minutes, 2 ml of purified methyl methacrylate (freshly distilled-from greenish yellow color tri-emylaluminium-methyl methacrylate complex) was transferred by stainless steel capillary under stirring using pure nitrogen presure and the polymerization was performed at -40 °C for 15 min. The reaction was terminated by adding degassed methanol. The polymer was recovered by precipitation into 400 mL of n-hexane. The crude polymer was dried at 40 °C for four hours under vacuum giving 1.86 gm of poly (methyl methacrylate) (100% conversion). Gel permeation chromatography equipped with 100 A, 500 A, 103 A, 104 A and one linear ji-ultrastyragel columns showed that the polymer had Mn,cpc = 25,000 g/mol and Mw/Mn = 1.09. Example 4 Polymerization of methyl methacrylate in tetrahydrofuran using 1,1-diphenylhexyllithium (DPHLi)-bislithium salt of triethylene glycol initiator system at -20 °C: Monomer resumption experiment. Into a flame dried 250 mL round bottom flask equipped with magnetic needle, nitrogen/vacuum three-way adapter with rubber septum, was added 120 mL dry tctrahydrofuran. A tctrahydrofuran solution of 1,1-diphcnylhexyllithium (DPHLi, -0.08M) was added drop wise under stirring until the initiator color persisted. 0.7 mL of ~O.OSM of initiator solution was required to get a persistent color. Then, 1.52 x 10"4 mol of DPHLi in THF solution (1 mL) was added and the reaction flask was cooled to -20 °C. A tctrahydrofuran solution (14 mL) containing 7.6 xlO"4 mole of bislithium salt of triethylene glycol was added into the above initiator solution. After few minutes, purified methyl methacrylate (freshly distilled from greenish yellow color triethylaluminium-methyl methacrylate complex) was added in 2 ml doses with a time interval of 5 min for each monomer dose. Before adding the next monomer dose, a small amount of sample was withdrawn from the reaction mixture for analysis and terminated with degassed methanol. A linear increase of the Mn,opc of PMMAs upon incremental addition of monomer with 100 % conversion has been observed. A plot of Mn>0pc vs conversion, in the drawing accompanying the specification, shows a straight line which is very close to the theoretically calculated, MnjCAL from the feed ratios of monomer to initiator. MWD of the obtained PMMAs remain same throughout the chain extension reaction (Mw/Mn = 1.7). Quantitative monomer conversion was obtained in every dose of monomer. Example 5 Polymerization of lauryl methacrylate in tetrahydrofuran using 1,1-diphenylhexyllithium (DPHLi)-bislithium salt of triethylene glycol initiator system at -40 °C Into a flame dried 250 mL round bottom flask equipped with magnetic needle, nitrogen/vacuum three-way adapter with rubber septum, was added 30 mL dry tetrahydrofuran. A tetrahydrofuran solution of 1,1-diphenylhexyllithium (DPHLi, -0.08M) was added drop wise under stirring until the initiator color persisted. Then, 1.2 x 10"4 mol of DPHLi in THF solution was added and the reaction flask was cooled to -40 °C. A tctrahydrofuran solution (5.3 mL) containingl.2 xlO"3 mole of bislithium salt of triethylcne glycol was added into the above initiator solution. After few minutes, 2.8 ml of purified lauiyl methacrylate (purified by passing through alumina column after treating with triethylaluminium) was transferred by stainless steel capillary under stirriim using pure nitrogen presure and the polymerization was performed at -40 °C for 15 min. The reaction was tenninated by adding degassed methanol. The polymer was recovered by removing solvent under vacuum and the residue was dissolved in benzene and freeze-dried. Poly (lauryl methacrylate) with quantitative conversion was obtained. GPC showed that the polymer had Mn.GPC = 28,000 g/mol with respect to PMMA standards and Mw/Mn = 1.16. Example 6 Block copolymerization of MMA and LMA using DPHLi-bislithium salt of triethylene glycol initiator system in THF at -40 °C Into a flame dried 250 mL round bottom flask equipped with magnetic needle, nitrogen/vacuum three-way adapter with rubber septum, was added 73 mL dry tetrahydrofuran. A tetrahydrofuran solution of 1,1-diphenylhexyllithium (DPHLi, -0.08M) was added drop wise under stirring until the initiator color persisted. Then, 1.2 x 10"4 mol of DPHLi in THF solution was added and the reaction flask was cooled to -40 °C. A tetrahydrofuran solution (14 mL) containing 1.2 xlO'3 mole of bislithium salt of triethylene glycol was added into the above initiator solution. First, 2.1 grams of MMA was polymerized. After 15 mins, 1.56 grams of LMA was added into living poly (methyl methacrylate) anion and the reaction was terminated after 15 mins with degassed methanol and the diblock copolymer was recovered after removing solvent by vacuum. The residue was dissolved in benzene and frceze-dried to give 3.367 grams of poly (MMA4>LMA) copolymcr (92 % conversion). GPC showed that the polymer had Mn,(;K: = 33,500 g/mol and M*/Mn= 1.08 Example 7 Polymerization of methyl methacrylate in tetrahydrofuran using 1,1-diphenylhcxyllithium (DPHLi)-bislithium salt of diethylene glycol initiator system at -20 °C Into a flame dried 250 mL round bottom flask equipped with magnetic needle, nitrogen/vacuum three-way adapter with rubber septum, was added 80 mL dry tetrahydrofuran. A tetrahydrofuran solution of 1,1-diphenylhexyllithium (DPHLi) was added drop wise under stirring until the initiator color persisted. Then, 1.8 x 10"1 mol of DPHLi in THF solution was added and the reaction flask was cooled to -20 °C. A tetrahydrofuran solution (20 mL) containing 1.8 xlO"J mole of bislithium salt of triethylene glycol was added into the above initiator solution. After few minutes, 3 ml of purified methyl methacrylate (freshly distilled from greenish yellow color tri-ethylaluminium-methyl methacrylate complex) was transferred by stainless steel capillary under stirring using pure nitrogen presure and the polymerization was performed at -20 °C for 15 min. The reaction was terminated by adding degassed methanol. The polymer was recovered by precipitation into 400 mL of n-hexane. The cnide polymer was dried at 40 °C for four hours under vacuum giving 1.86 gm of poly (methyl methacrylate) (100% conversion). Gel permeation chromatography equipped with 100 A, 500 A, 103 A, 104 A and one linear (.i-ultrastyragel columns showed that the polymer had M,,.GPC = 18,040 g/mol and Mw/Mn = 2.22. Example S (comparative example) Polymerization of methyl methacrylate in tetrahydrofuran using 1,1-diphenylhexyllithium (DPHLi) as initiator at 0 °C Into a flame dried 250 ml round bottom flask equipped with magnetic needle, nitrogen Vacuum three-way adapter with rubber septum, was added 100 mL dry tctrahydrofu-ui. A tetrahydroluran solution of 1,1-diphenylhexyllithitim (DPHLi, -O.OSM) was added drop wise under stirring until the initiator color persisted. 0.6 mL of -0.08M of initiator solution was required to get a persistent color. Then, 4 ml of THF solution containing 2.0 x 10"* mol DPHLi was added and the reaction flask was cooled to 0°C using ice bath. After few minutes, 3.5 ml of purified methyl methacrylate (freshly distilled from greenish yellow color tri-ethylalurdnium-methyl methacrylate complex) was transferred by stainless steel capillary under stirrinc using pure nitrogen presure and the polymerization was performed at 0 °C for 15 min. The reaction was terminated by adding degassed methanol. The polymer was recovered by precipitation into 400 mL of n-hexane. The crude polymer was dried at 40 °C for four hours under vacuum giving 2.62 gm of poly (methyl methacrylate) (80% conversion). Gel permeation chromatcgraphy equipped with 100 A, 500 A, 103 A, 104 A and one linear (i-ultrastyragel columns showed that the polymer has Mn,cpc = 26,630 g/mol and Mw/Mn = 1.67. However, the theoretically calculated Mn.cai = 16,480 g/mole. Example 9 (comparative example) Polymerization of methyl methacrylate in tetrahydrofuran using 1,1-diphenylhexyllithJum (DPHLi) as initiator in the presence of lithium 2-(2-methoxyethoxy) ethoxide in THF at -20 °C Into a flame dried 250 mL round bottom flask equipped with magnetic needle, nitrogen/vacuum three-way adapter with rubber septum, was added 90 mL dry tetrahydrofuran. A tetrahydrofuran solution of 1,1-diphcnylhcxyllithium (DPHLi,-0.08M) was added drop wise under stirring until the initiator color persisted. Then, 1.0 x 10'4 mol of DPHLi in THF solution was added and the reaction flask was cooled to -20 °C. A tetrahydrofuran solution (11 mL) containingl.O xlO'3 r.ole of lithium 2-(2-mcthoxyethoxy) ethoxide was added into the above initiator solution. After iVv minutes, 2.5 ml of purified methyl methacrylate (freshly distilled from greenish yellow color tr.-ethylaluminium-methyl methacrylate complex) was transferred by stainless steel capillary cider stirring using pure nitrogen presure and the polymerization was performed at -20 °C for 15 min. The reaction was terminated by adding degassed methanol. The polymer was recovered by precipitation into 400 mL of n-hexane. The crude polymer was dried at 40 °C for four hours inder vacuum giving 1.86 gm of poly (methyl methacrylate) (100% conversion). Gel permeation ciromatography equipped with 100 A, 500 A, 103 A, 104 A and one linear u,-ultrastyragel cc'.umns showed that the polymer had Mn,opc = 23,700 g/mol and Mw/Mn = 1.91. Advantages of the invention: 1 Controlled anionic polymerization of alkyl (meth)acrylates can be conveniently carried out in batch at higher temperatures like -20 °C, 0 °C and 30 °C. 2 Controlled anionic polymerization of alkyl (meth)acrylates can be carried out either in polar, non polar medium or the mixture of these solvents. We Claim: 1. An improved process for the preparation of poly alkyl (meth)acrylate which comprises preparing an organolithium initiator - additive complex of general formula (I), as shown in the drawing accompanying the specification, where RI = linear or branched alkyl group having one to six carbon atoms, R2 = phenyl or alkyl group having one to six carbon atoms, R3 = phenyl or an ester group, RA = alkyl group having two to three carbon atoms and n = 1 to 4 and M+ is an alkali or alkaline earth metal and M is a lithium atom, in a solvent such as herein described, wherein organolithium initiator and additive is in the range of 1 : 1 to 1 : 40, reacting the obtained organolithium initiator - additive complex with alkyl (meth) acrylate for anionic polymerization, in presence an organic solvent such as herein described, at temperature ranging -20°C to 0°C to obtain the polymer of alkyl (meth)acrylate, recovering the polymer using non-solvent by conventional precipitation method such as herein described to get the desired poly alkyl (meth) acrylate. 2. An improved process as claimed in claim 1, wherein the solvent used for preparing solution of organolithium initiator - additive is selected from tetrahydrofuran (THF), tetrahydropyran (THP) or a mixture of tetrahydrofuran and an aromatic hydrocarbon. 3. An improved process as claimed in claim 1-2, wherein the alkyl (meth)acrylates used is selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, lauryl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate and t-butyl acrylate. 4. An improved process as claimed in claim 1-3, wherein the additive is selected from bismetal salts of mono, di- or tri-ethylene glycols. 5. An improved process as claimed in claim 1 to 4 wherein the preferred ratio of organolithium initiator to additive is 1 : 10. 6. An improved process as claimed in claim 1 to 5 wherein the organic solvent used is selected from benzene, toluene, zylene, ethylbenzene, mesitylene and tetralin preferably toluene. 7. An improved process for the preparation of poly alkyl (meth)acrylate substantially as herein described.

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1495-del-1999-abstract.pdf

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