FR2913979A1 - PROCESS FOR THE PREPARATION OF POLYMERS WITH NITROXIDE FUNCTIONS - Google Patents

Abstract

The present invention relates to the synthesis of polymers with nitroxide functions by oxidation of the corresponding amine functional precursor, more particularly the subject of the invention is a process for the preparation of a 2,2,6,6-tetraalkylpiperidinyloxy poly (meth) acrylate by oxidation of the 2,2,6,6-tetraalkylpiperidine poly (meth) acrylate with a peracid at a controlled pH.

Description

1

  The present invention relates to the synthesis of polymers with nitroxide functions by oxidation of the corresponding amine functional precursor, more particularly the subject of the invention is a process for the preparation of a 2,2,6,6-tetraalkylpiperidinyloxy poly (meth) acrylate by oxidation of the 2,2,6,6-tetraalkylpiperidine poly (meth) acrylate with a peracid at a controlled pH. In the present invention, the term (meth) acrylate means a derivative of acrylic acid or methacrylic acid. Polymers with nitroxide functions are advantageously used to form rechargeable battery electrodes (US 2003/0096165). In particular, NAKAHARA K. et al in Chem. Phys. Lett. 359 (2002) 351-354 propose to use 2,2,6,6-tetramethylpiperidinyloxy polymethacrylate, hereinafter referred to as PTMA, to prepare a cathode of a rechargeable battery. The PTMA is obtained by oxidation with 3-chloroperbenzoic acid (mCPBA) of the polymer resulting from the free radical polymerization. monomer 2,2,6,6-tetramethylpiperidine methacrylate. Perbenzoic acids such as 3-chloroperbenzoic acid dissolved in organic solvents such as methylene chloride are known to effectively oxidize many secondary amines nitroxides (Journal of American Chemical Society, 1967, 89 (12) 3055 -3056). However, this process for the preparation of PTMA has many drawbacks: on the one hand, 3-chloroperbenzoic acid is an expensive raw material, on the other hand there is formation of chlorobenzoic acid as a by-product that is necessary to separate to obtain the PTMA with a purity adapted to its use, especially as a material for producing battery electrodes. This process for preparing the PTMA is thus difficult to use on an industrial scale. Oxygenated water - H2O2 - is known as an inexpensive oxidant and its use in the presence of catalysts for oxidizing secondary amines has been widely described in the state of the art. However, these hydrogen peroxide processes are applicable only to water-soluble amine / nitroxide pairs. When it comes to amine functional polymers, such as the PTMA precursor polymer, the substrate is not sufficiently soluble in water, which renders this oxidation method unusable. It is particularly interesting to have a process for preparing PTMA which overcomes these disadvantages. The proposed solution is to oxidize the secondary amine functions of the precursor polymer of the PTMA by means of aliphatic peracids in two-phase organic solvent / water with a pH of the controlled aqueous phase. This oxidation method is described in WO 00/40550 of the Applicant Company for oxidizing secondary amines (or secondary polyamines) hindered or those having a -CH a to the nitrogen atom. The compounds oxidized according to this method are secondary amines or polyamines of low molecular weight, generally with a mass of less than 5000, such as, for example, the polyamine known under the name CHIMASSORB 944 which has a molecular weight of 3000.

  It has now been discovered that this method can be used to oxidize amine functional polymers such as 2,2,6,6-tetraalkylpiperidine poly (meth) acrylates, which have a significantly higher molecular weight, for example 10,000 or more, while keeping good kinetics of reaction despite the accessibility difficulties of the reactive sites of these polymers.

  The oxidation reaction with aliphatic peracids furthermore has the advantage of being carried out with inexpensive, commercially available oxidants under mild conditions, rapidly and with high yields. In addition, the purification of the nitroxide functional polymer obtained is simple and the effluents (organic acid salts) can be optionally recovered. The subject of the present invention is therefore a process for preparing a nitroxide functional polymer from the corresponding secondary amine functional monomer comprising the following steps: a) a secondary amine functional polymer is prepared by mass solution polymerization in emulsion or suspension of a 2,2,6,6-tetraalkylpiperidine (meth) acrylate, 3

  b) the polymer is solubilized with an organic solvent, immiscible with water, then water is added, c) then, simultaneously and with vigorous stirring, in the biphasic medium thus obtained, a quantity of aliphatic peracid in a ratio of peracid molar / secondary amine functions ranging from 1.5 to 3.5, preferably from 2 to 3, and a sufficient amount of a basic aqueous solution to obtain a pH of the aqueous phase of biphasic medium ranging from 4 to 12, at a temperature of between -10 ° C. and + 40 ° C., until complete conversion of the secondary amine functions, then d) the organic phase is recovered by simple decantation, and the polymer with nitroxide functions is isolated by evaporation of the organic solvent under pressure scaled down. According to the present invention, the organic solvent must be immiscible with water, inert with respect to the reactants and the products and have a good solvent power of the reagents and products obtained. By way of illustration of such organic solvents which can be used according to the present invention, mention may be made of aliphatic or cycloaliphatic hydrocarbons such as pentane, hexane, heptane, decane, cyclohexane and cyclododecane; aromatic hydrocarbons such as benzene, toluene, xylenes; chlorinated hydrocarbons such as methylene chloride, 1,2-dichloroethane, chloroform, chlorobenzene; esters of aliphatic acids such as ethyl acetate, ethyl propionate or a mixture of at least two of the abovementioned solvents.

  By way of illustration of aliphatic peracids which can be used according to the present invention, mention may be made of peracetic acid, perpropionic acid and perbutanoic acid. Preferably, peracetic acid or perpropionic acid will be used. The process of the present invention first consists of preparing a 2,2,6,6-tetraalkylpiperidine poly (meth) acrylate. The polymerization of 2,2,6,6-tetraalkylpiperidine (meth) acrylate can be carried out according to a method 4

  radical solution, mass, emulsion or suspension according to methods well known to those skilled in the art. More particularly, the polymerization of 2,2,6,6-tetraalkylpiperidine (meth) acrylate in bulk with a free radical initiator such as an organic peroxide or an azo compound will be carried out. In the process according to the invention, it will be sought to obtain a polymer with a number-average molecular weight ranging from 5,000 to 200,000, preferably from 7500 to 100,000, in particular from 7500 to 50,000. The process of the present invention then consists of to solubilize, with stirring, the 2,2,6,6-tetraalkylpiperidine poly (meth) acrylate in an organic solvent, immiscible with water and inert with respect to the amine functions of the polymer and the reagents implemented. The amount of organic solvent used is a function of the solubility of the polymer in said solvent, and depends in particular on the molecular weight of the polymer. This amount of organic solvent is not critical and can vary to a large extent. However, for economic reasons and in a concern for the environment, a person skilled in the art will endeavor to choose an organic solvent (or a mixture of solvents) so as to use only minimum amounts to solubilize the polymer. To the organic solution is added, with stirring, water and then added simultaneously with vigorous stirring, the biphasic medium obtained aliphatic peracid, generally in solution in the corresponding aliphatic acid, in a molar ratio peracid / secondary amine as defined above and a sufficient amount of a basic aqueous solution such that the pH of the aqueous solution of the biphasic medium is maintained at a value ranging from 4 to 12 and preferably from 5 to 9. The basic aqueous solution may be a solution of an alkali metal or alkaline earth metal carbonate or hydrogencarbonate, or an alkali metal hydroxide solution or an alkali metal hydroxide solution. earthy, such as sodium hydroxide, potassium hydroxide, calcium hydroxide or magnesium hydroxide.

  According to the present invention, use will preferably be made of a basic aqueous solution of an alkali metal carbonate or hydrogencarbonate. By way of illustration of alkali metal carbonates or hydrogen carbonates which may be used according to the present invention, mention may be made of NaHCO 3, KHCO 3, K 2 CO 3 and Na 2 CO 3. It is also possible to use ammoniacal solutions. The concentration by weight of aqueous solutions of carbonates or hydrogenocarbonates of alkali or alkaline earth metals is determined by the solubility limit of these species in water. Efforts will be made to use the most concentrated solutions possible. The oxidation reaction of the secondary amine functions to nitroxide functions is carried out at a temperature ranging from -10 ° C. to + 40 ° C. and preferably ranging from -5 ° C. to + 30 ° C. until the secondary amines are totally transformed. The progress of the reaction can be followed by analytical methods such as the chemical determination of the peracid implemented according to methods known to those skilled in the art (assay with the potassium iodide and sodium thiosulfate method) and gas chromatography.

  It is preferably carried out at atmospheric pressure. When the reaction is complete, the organic phase is recovered, generally, by simple decantation. This organic phase may optionally be washed with demineralized water and then dried. The formed 2,2,6,6-tetraalkylpiperidinyloxy poly (meth) acrylate is isolated by evaporation of the organic solvent under reduced pressure. If necessary, the purity of the polymer can be improved by dissolution and reprecipitation. The invention also relates to the use of the nitroxide functional polymer obtained according to the process of the invention, for preparing battery electrodes or as a catalyst for the oxidation of alcohols.

  The process according to the invention is particularly well suited for preparing the PTMA according to the following reaction scheme: ## STR1 ## with n being able to range from 20 to 800, preferably from 30 to 500, more particularly 40 to 100.

  The following examples illustrate the present invention without, however, limiting its scope.

  EXAMPLES 2,2,6,6-Tetramethylpiperidine methacrylate (commercially available from Asahi Denka under the reference LA-87) is used as the secondary amine monomer.

  Mass radical polymerization initiated by AIBN (2,2'-azobisisobutyronitrile) is carried out to obtain a tetramethylpiperidine polymethacrylate having a mass Mn = 10,000 g / mol. In a 500 ml double-jacketed reactor equipped with anchor-type stirring, 2 casting ampoules, a temperature probe and a pH probe, 10 g of tetramethylpiperidine polymethacrylate, 100 g of dichloromethane and 50 g of water. 23.8 g of peracetic acid at 40% (0.125 mol) and 60 g of a 35% aqueous solution of potassium carbonate are added simultaneously in the course of 30 minutes at 20 ° C. with stirring. The addition is carried out so that the pH of the aqueous phase is maintained between 7 and 7.4. At the end of casting, it is allowed to react for 2 hours at ambient temperature, then the pH is increased to 9 by addition of potassium carbonate (35% aqueous solution). Let's decant. The organic phase is recovered, washed with 50 g of water and then the dichloromethane is evaporated off under reduced pressure. 9.2 g of a paramagnetic orange solid are obtained.

Claims (6)

  A process for preparing a nitroxide functional polymer from the corresponding secondary amine functional monomer comprising the following steps: a) a secondary amine functional polymer is prepared by mass solution, emulsion or suspension polymerization of a 2,2,6,6-tetraalkylpiperidine (meth) acrylate, b) the polymer is solubilized with an organic solvent, immiscible with water, then water is added, c) then added simultaneously and under strong stirring in the biphasic medium thus obtained, an amount of aliphatic peracid in a peracid / secondary amine functions molar ratio ranging from 1.5 to 3.5, and a sufficient amount of a basic aqueous solution to obtain a pH of the aqueous phase biphasic medium ranging from 4 to 12, at a temperature between -10 C and +40 C, until complete conversion of secondary amine functions, then d) recovering the organic phase by simple decantation, and isolating the nitroxide functional polymer by evaporation of the organic solvent under reduced pressure.   2. Method according to claim 1, characterized in that the molar ratio peracid / secondary amine functions ranges from 2 to   3. 3. Method according to claim 1 or 2, characterized in that the pH of the aqueous phase of the biphasic medium is from 5 to 9.   4. Process according to any one of the preceding claims, characterized in that the polymer resulting from step (a) has a mass ranging from 5,000 to 200,000, preferably from 7500 to 100,000.   5. Method according to any one of the preceding claims, characterized in that the monomer is 2,2,6,6-tetramethylpiperidine methacrylate.   6. Use of the nitroxide functional polymer obtained by the process of any one of the preceding claims for preparing battery electrodes or as an alcohol oxidation catalyst.