PROCESS FOR THE SYNTHESIS OF POLYEPICHLORHYDRIN

Abstract

The invention relates to a process for the synthesis of polyepichlorohydrin which comprises: a) the reaction of epichlorohydrin with boron trifluoroetherate in the presence of a solvent; b) the addition of epichlorohydrin to the product of the reaction obtained in step a); c) the hydrolysis of the product obtained in step b).

Description

Title of the invention: Process for the synthesis of polyepichlorohydrin Field of invention

[0001] The invention relates to the field of energy materials. More specifically, the invention relates to a method for synthesizing an intermediate of glycidyl polyazide, namely polyepichlorohydrin. State of the art

[0002] With the aim of increasing the ballistic performance of tactical and strategic missiles, more energetic materials have been developed, notably using polyglycidyl azide (PAG) to replace the inert binders historically used such as polybutadienehydroxytelechelic acid (PBHT).

[0003] PAG can be produced in two steps, according to scheme 1 below, from epichlorohydrin (ECH), via the intermediary of polyepichlorohydrin (PECH), which is a dihydroxytelechelic polymer. Diagram 1: Summary of the PAG

[0004] ™ b CHAOHCHOHCHsa CH2N3 ECH PECH PAG

[0005] In the literature, there are three main methods of polymerization of ECH to obtain PECH:

[0006] - coordination polymerization; - cationic polymerization;

[0007] - anionic polymerization.

[0008] Coordination polymerization

[0009] The catalytic ring-opening polymerization of ECH was first described by Vandenberg [1-4] to synthesize PECHs with high molecular weights (Mn > 50,000 g.mol *).

[0010] More recently other active species have been described such as bis(q-oxo)dialkylaluminum [5]. Several other monometallic [6-8] and bimetallic

[15] catalytic systems have also been described, but again for the synthesis of high molecular weight PECH.

[0011] Generally speaking, coordination polymerization has some drawbacks. beneficial from the point of view of understanding the mechanisms:

[0012] - Unsimple catalytic systems and polymerization procedures; - No data on polydispersity, functionality or structure;

[0013]

[0014]

[0015] - Unknown polymerization mechanism. A more recent publication

[10] describes the solvent-free polymerization of ECH in the presence of a specific catalyst [Zn-Co(III) DMCC: “Zinc cobalt(III) double metal cyanide complex”] as described in Scheme 2 below. The yields vary from 30 to 84% for number-average masses of 900 g.mol1 to 4200 g.mol1, however, with a high polydispersity of the order of 1.5. Scheme 2: Coordination polymerization of ECH ZrvCo (111} DMCC h.î ------------------------------------------------------------ ' XCi

[0016] y ■2«' Zn-Co (III) DMCC

[0017]

[0018]

[0019] Anionic polymerization The controlled anionic polymerization of ECH in the presence of Oct4NBr / (iBu)3Al as initiator was described by Carloti [11-12]. It has many advantages, including the use of a non-chlorinated solvent such as toluene. But it also has a major disadvantage which is the production of a mono-hydroxyl polymer as shown in Scheme 3 below. Scheme 3: Anionic polymerization of ECH Br— initiation cwnijÿltx ~ X Ht y 1.......<. ...........*" Br—CHi—ÇH—O— \ g, j-Bu pO...... CiCSf / ' M Brl-CHv-ÇH-O-ï H pd¥C|^dü9i«hŸ^îu Cs-iCI

[0020] Very recently, direct polymerization of glycidyl azide has been carried out with triethylborane combined with tetrabutylammonium bromide as catalyst

[13] . Cationic polymerization

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031] Literature data clearly show that coordination polymerization and anionic polymerization are not suitable for the synthesis of PECH, mainly due to a lack of control of the molecular mass and a functionality very often very far from the target value: 2. In contrast, cationic ring-opening polymerization with a diol as initiator leads to a dihydroxytelechelic polymer as shown in Scheme 4. Diagram 4: Polymerization of ECH Step 1 - Preparation of the catalytic complex HO x H Step 2 - Slow addition of the monomer ŒjCHOH CH H Polymerization is often carried out in the presence of Lewis acids, such as boron trifluoroetherate (BF3OEt2) [14-18], tin tetrachloride (SnCl4)

[19] , triethyloxonium hexafluorophosphate (Et3O+PF6)

[20] , 1,4-butanediyl ditriflate

[21] . Triethyloxonium hexafluorophosphate leads to PECHs with low molecular weights (Mn < 1000 g.moF1), butanediyl ditriflate leads to PECHs with higher molecular weights (between 3500 and 15000 g.moF1) but with low yields. Boron trifluoroetherate and tin tetrachloride are the most widely used, often combined with a diol as an initiator, with boron trifluoroetherate providing less polydisperse polymers than those obtained with tin tetrachloride. Two patent applications [22,23] also describe the production of PECH by cationic polymerization. The most commonly used solvents for ECH polymerization are chlorinated solvents, such as methylene chloride or 1,2-dichloroethane (DCE). The use of such solvents is impacted by European Regulation No. 1907 / 2006, better known as the REACH regulation (acronym for "Registration, Evaluation, Authorization and Restriction of Chemicals"), which lists substances whose use is subject to authorization. For example, DCE has been included in Annex XIV of the REACH regulation since August 14, 2014, and has been unusable without authorization since November 22, 2017. The obsolescence of DCE, and other chlorinated solvents, is therefore expected in the short to medium term.

[0032] The replacement of chlorinated solvents in the synthesis of PECH therefore involves the search for alternative synthesis routes, compatible with the environmental and toxicological regulations currently in force, while making it possible to preserve the characteristics (number average mass Mn, weight average mass Mp and hydroxyl content) of the polymers currently produced and used on an industrial scale.

[0033] There are certainly examples of solvent-free cationic polymerization of ECH described in the literature. The first example is the polymerization of ECH in the presence of Bronsted acid such as acid clays

[24] . In this case, the polymerization is carried out without solvent but the polymer obtained is bimodal, with a low molecular weight and a significant presence of cyclic by-products. In the second example, the reaction takes place in the presence of paratoluenesulfonic acid

[25] and tin tetrachloride. This solvent-free route, however, presents a major problem which is the risk of loss of control of the reaction.

[0034] The possibility of obtaining PECH in a non-chlorinated solvent has been studied using butanediol as a polymerization initiator and boron trifluoroetherate as a catalyst. However, this butanediol / boron trifluoroetherate system has several disadvantages:

[0035] - need for a significant quantity of catalyst to reduce the exothermicity of the reaction ;

[0036] - existence of an induction period followed by a "spontaneous" increase in the temperature, sometimes difficult to control;

[0037] - competition between butanediol and residual water present in the reagents, which leads to the formation of a PECH with high polydispersity and especially to non-optimal functionality, denoting the presence of macrocycles within the polymer.

[0038] None of the processes described in the literature are therefore truly satisfactory with regard to the regulations in force. Those which could be considered acceptable with regard to these regulations have low yields or lead to polymers whose physicochemical characteristics are not consistent with those of the polymers currently produced on an industrial scale.

[0039] There is therefore a need to have an alternative synthesis of PECH, which is more environmentally friendly, compatible with current regulations, and which does not alter the physicochemical properties of this product. It is with these specifications in mind that the present invention was developed. Summary of the invention

[0040] The invention relates to a process for the synthesis of polyepichlorohydrin which comprises:

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056] (a) the reaction of epichlorohydrin with boron trifluoroetherate in the presence of a polymerization initiator and optionally a non-chlorinated solvent; b) adding epichlorohydrin to the reaction product obtained in step a); c) hydrolysis of the product obtained in step b). Detailed description of the invention The invention relates to a method for synthesizing polyepichlorohydrin which implements a cationic polymerization of epichlorohydrin by ring opening according to a mechanism called "activated monomer". In this mechanism, shown in Scheme 5, the chain ends are neutral and the propagation takes place via the nucleophilic attack of a hydroxyl group on the oxonium ion present in the monomer, thus forming, only, a linear PECH diol. Diagram 5: Activated monomer mechanism In order to control the molar mass of PECH, the polymerization proceeds essentially in two phases: Phase 1: initiation of polymerization by bringing together epichlorohydrin, boron trifluoroetherate, a polymerization initiator, and possibly a non-chlorinated solvent; Phase 2: polymerization by controlled addition of epichlorohydrin. The termination phase of the polymerization proceeds in a conventional manner in the presence of water. Thus, the present invention relates to a process for the synthesis of polyepichlorohydrin which comprises: (a) the reaction of epichlorohydrin with boron trifluoroetherate in the presence of a polymerization initiator and optionally a non-chlorinated solvent; b) adding epichlorohydrin to the reaction product obtained in step a); c) hydrolysis of the product obtained in step b). In some embodiments, the polymerization initiator is water, butanediol or 3-chloro-1,2-propanediol, preferably water. In some embodiments, the non-chlorinated solvent is toluene, acetonitrile or nitromethane, preferably toluene. In some embodiments, the polymerization initiator and epichlorohydrin are used in substantially equimolar amounts in step a). In some embodiments, the polymerization initiator is used in excess compared to boron trifluoroetherate in step a).

[0058] In some embodiments, epichlorohydrin is used pure or in a solvent in step b). In some embodiments, said solvent is identical to that used in step a).

[0059] In certain embodiments, the epichlorohydrin is added in one or more times in step b).

[0060] In certain embodiments, the reaction of step a) is controlled to obtain an epichlorohydrin oligomer having a degree of polymerization (DPn) greater than or equal to 4. When the oligomer of DPn > 4 is isolated at the end of step a), step b) may further comprise the addition of boron trifluoroetherate.

[0061] The process according to the invention is compatible with scaling up (pilot and / or industrial scale). Indeed, this process makes it possible to obtain polyepichlorohydrin on a scale of around one hundred grams (see examples 4 and 6) without degradation of the characteristics of the polymer in terms of Mn, polydispersity and functionality, nor any risk linked to the exothermicity of the reaction.

[0062] In summary, the synthesis process of the invention allows very good control of the polymerization and has numerous advantages:

[0063] - control, or even elimination, of the temperature exotherm often observed during cationic ring-opening polymerization;

[0064] - polymerization carried out between 20°C and 40°C in a non-chlorinated solvent, in the presence of water;

[0065] - polymerization time (approximately 5 to 6 hours) compatible with an in scale industrial;

[0066] - polymerization yields greater than 90% or even quantitative therefore com comparable to the yields obtained on an industrial scale which are of the order of 95%;

[0067] - obtaining a monomodal polymer with perfectly controlled Mn (from 500 at 4100 g.mol *) having an exceptionally high functionality of 2.00 ± 0.05, therefore in accordance with theory, to be compared with a functionality of 1.4 to 1.6 for a PECH produced, to date, on an industrial scale;

[0068] - low polydispersity, less than or equal to 1.25 which is therefore comparable to the values measured on an industrial PECH.

[0069] The invention will be better understood with the aid of the following examples, given for illustrative purposes. In these examples, the number-average (Mn) and weight-average (Mp) molar mass of polyepichlorohydrin was determined either by NMR or by size exclusion chromatography (SEC) using the following devices: NMR *H NMR (500 MHz) in CDC13 at 25°C on a Bruker AC-500 instrument; 13C NMR (125 MHz) in DMSO-d6 on a Bruker AC-500 instrument. DRY

[0071] - Equipment: Ultimat 3000 Thermo Scientific with an Agilent PLgel 5 pm MIXED-C column (300X7.5 mm) and a precolumn (PL gel 5 pm 50X7.5 mm) thermostated at 30°C; - Detection: refractometry and UV; - Eluent: THF, 1.0 ml / min; - Standard: polystyrene.

[0072] The polydispersity D of polyepichlorohydrin is equal to the ratio Mp / Mn.

[0073] The functionality is calculated according to the formula: [Mn(SEC) / Mn(RMN)]x2.

[0074] The formulas BF3O(C2H5)2 and BF3OEt2 are used interchangeably to designate boron trifluoroetherate (also called boron trifluoride dietherate). Example 1

[0075] a) 0.48 mL (6.12x103 mol) of ECH, 0.046 mL (3.72x104 mol) of BF3O(C2H5)2 and 0.1 mL (5.56x103 mol) of H2O were introduced into a flask. The reaction mixture was stirred at 25°C for 1.5 h until a transparent viscous liquid was formed. Then, a mixture of 11.3 mL (0.15 mol) of ECH and 5.65 mL of toluene was added via a syringe pump, controlling the addition rate to control the exothermicity of the reaction.

[0076] b) After total addition of the ECH, the reaction mixture was stirred for 1 h, then hydrolyzed by the addition of 2 to 3 mL of distilled water. The reaction medium was diluted with toluene (approximately 5 mL), washed with approximately 50 mL of an aqueous solution of sodium bicarbonate (at 5% by mass) and several times with distilled water (approximately 50 mL in total) until the washing phases were neutral. The solvent was evaporated under vacuum using a rotary evaporator and the polyepichlorohydrin obtained was dried under vacuum at 60°C to constant weight.

[0077] Yield > 97%; Mn (NMR) = 2500 g.moF1; Mn (SEC) = 2600 g.moF1; D = 1.1 / 1.2; Functionality = 2. Example 2

[0078] The procedure of Example 1 was repeated but using 12.7 mL (0.17 mol) of ECH, 0.054 mL (0.44x103 mol) of BF3OEt2 and 1.84 mL (6.54x103 mol) of 3-chloro-1,2-propanediol.

[0079] Yield = 94%; Mn (NMR) = 2340 g.moF1; Mn (SEC) = 2370 g.moF1; D = 1.20; Functionality = 2. Example 3

[0080] The procedure of Example 1 was repeated using, in the second part of step a), pure ECH instead of ECH in solution in toluene.

[0081] Yield = 99-100%; Mn (NMR) = 2270 g.mol1; Mn (SEC) = 2270 g.mol1; D = 1.23; Functionality = 2. Example 4

[0082] 3.2 mL (4.08x102 mol) of ECH, 0.33 mL (2.71x103 mol) of BF3OEt2, 3.2 mL of toluene and 0.73 mL (4.05x102 mol) of H2O were introduced into a flask. The reaction mixture was stirred for 1.5 h at 25°C until a clear viscous liquid was formed. Then, a mixture of 80.7 mL (1.03 mol) of ECH and 37 mL of toluene was added in two portions to the flask, each time controlling the addition rate to control the exothermicity of the reaction. The cumulative addition time of the ECH solution was approximately 9 h. Once the ECH solution was added, the reaction mixture was again stirred for 1 h and then hydrolyzed. The washings and recovery of the polyepichlorohydrin were carried out according to the procedure of Example 1.

[0083] Yield = 97%; Mn (NMR) = 2430 g.mol1; Mn (SEC) = 2580 g.mol1; D = 1.18; Functionality = 2. Example 5

[0084] An ECH oligomer was prepared, with stirring for 4 h, from 12.8 mL (4.08x102 mol) of ECH, 0.33 mL (2.71x103 mol) of BF3OEt2, 15.4 mL of toluene and 0.73 mL (4.05x102 mol) of H2O. The product obtained had the following characteristics:

[0085] Yield = 85%; Mn (SEC) = 622 g.mol1; Mn (NMR) = 425 g.mol1: D =1.09; DPn = 4.

[0086] A polymerization reactor was then charged with 12.64 g (2.97x102 mol) of the ECH oligomer, 37 mL of toluene and 0.27 mL (2.19x103 mol) of BF3OEt2. The reaction medium was stirred for 1 h, then 71 mL (0.91 mol) of ECH was added to the reactor. The reaction medium was again stirred for 1 h, then hydrolyzed. The washings and recovery of the polyepichlorohydrin were carried out according to the procedure of Example 1.

[0087] Yield = 99%; Mn (NMR) = 2500 g. mol1; Mn (SEC) = 2800 g.mol1; D = 1.21; Functionality = 2. Example 6

[0088] 3.2 mL (4.08x102 mol) of ECH, 0.32 mL (2.69x103 mol) of BF3OEt2, 3.2 mL of Toluene and 0.7 mL (3.85x102 mol) of H2O were introduced into a flask. The reaction mixture was stirred for 1.5 h. 78 mL (1.00 mol) of ECH were then added in two portions to the flask, each time controlling the rate of addition to control the exothermicity of the reaction. The cumulative addition time of ECH was approximately 8 h. Once the ECH solution was added, the reaction mixture was stirred again for 0.5 h and then hydrolyzed. The washings and recovery of polyepichlorohydrin were carried out according to the procedure of example 1.

[0089] Yield = 99%; Mn (NMR) = 2490 g.mol1; Mn (SEC) = 2820 g.mol1; D = 1.21; Functionality = 2. Bibliographic references

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Claims

Claims

1. A process for the synthesis of polyepichlorohydrin which comprises: a) reacting epichlorohydrin with boron trifluoroetherate in the presence of a polymerization initiator and optionally a non-chlorinated solvent; b) adding epichlorohydrin to the reaction product obtained in step a); c) hydrolyzing the product obtained in step b).

2. A process according to claim 1, wherein the polymerization initiator is water or 3-chloro-1,2-propanediol, preferably water.

3. The method of claim 1, wherein the non-chlorinated solvent is toluene.

4. A process according to any one of claims 1 to 3, wherein the reaction of step a) is carried out in the presence of equimolar amounts of polymerization initiator and epichlorohydrin.

5. Process according to any one of claims 1 to 4, in which the reaction of step a) is carried out in the presence of an excess of polymerization initiator relative to the boron trifluoroetherate.

6. A process according to any one of claims 1 to 5, wherein in step b) the epichlorohydrin is used pure or in a solvent, preferably the same solvent as that used in step a).

7. A method according to any one of claims 1 to 6, wherein the epichlorohydrin is added one or more times in step b).

8. A process according to any one of claims 1 to 5, wherein the reaction is controlled in step a) to obtain an epichlorohydrin oligomer having a degree of polymerization greater than or equal to A

9. *T. A process according to reaction 8, wherein the oligomer obtained in step a) is isolated and step b) further comprises adding boron trifluoroetherate to said isolated oligomer.