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 polymerization initiator; b) the addition of a good solvent for epichlorohydrin to the reaction product obtained in step a); c) the addition of epichlorohydrin to the reaction product obtained in step b).

Description

Description Title of the invention: Process for the synthesis of polyepichlorohydrin Scope of the invention

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

[0002] — With the aim of increasing the ballistic performance of tactical missiles and Strategically, more energy-efficient materials have been developed, particularly in using glycidyl polyazuride (PAG) as a replacement for inert historical binders commonly used such as polybutadiene hydroxytelechelic acid (PBHT).

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

[0004] CHIOHCHOHCHaCI NaNs ___0H2C} Xe ÔÈ He 0-0H-0H2 OH {CH2C}; 4 | has H--O}-CH--CH;O;-H | CHaNa - a È i CHAN- # se ja | CHaNS 1 EGH PECH PAG

[0005] — In the literature, there are three main methods for polymerizing ECH to obtain the PECH:

[0006] - coordination polymerization; cationic polymerization;

[0007] - anionic polymerization.

[0008] = Coordination polymerization

[0009] — Ring-opening catalytic polymerization of ECH has been described for the first time by Vandenberg [1-4] to synthesize PECH with molecular weights high cular (Mn > 50,000 g.mol-!).

[0010] = More recently, other active species have been described, such as the bis(u-oxo)dialkylaluminum [5]. Several other mono- catalytic systems tallic [6-8] and bimetallic

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

[0011] = In general, coordination polymerization presents some incons- Venients from a point of view of understanding the mechanisms:

[0012] - Catalytic systems and somewhat simple polymerization procedures; No data on polydispersity, functionality or structure; Polymerization mechanism unknown. 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(II) double metal cyanide complex"] as shown in Scheme 2 below. Yields range from 30 to 84% for average number masses of 900 g·mol⁻¹ to 4200 g·mol⁻¹, with, however, a high polydispersity, on the order of 1.5. Scheme 2: Polymerization of ECH by coordination Z-Co (1) DMCC Aa Zn-Co (I) DMCC _H in SRE ci ; Nu PNT é —mRe., pe c97 7 Can He MF A ue ca mo can À sc Can” 'ençon A; 75 50 AN RAA Zn-Co ill) CMCC Anionic polymerization The controlled anionic polymerization of ECH in the presence of Oct,NBr / (iBu)sAl as an initiator was described by Carloti [11-12]. It offers numerous advantages, notably the use of a non-chlorinated solvent such as toluene. However, it also has a major drawback: the formation of a mono-hydroxyl polymer, as shown in Scheme 3 below. Scheme 3: Anionic polymerization of ECH Br— Abuse “NOR lsétixting coraples farmalian Br "NO, RSNERRR: « —— Br-CH-CH-0"aW-Bu;l" “NO, « AG-Au) Mit _ ae us AIi-Bu}; Cruecl ® +80 Do "maCriDu viens Da meonamer actkader propagatedon * srmaleathon paivepiæhioronydrir Brfcre- çh-0) # eng * Very recently, the direct polymerization of glycidyl azide was achieved with triethylborane combined with tetrabutylammonium bromide as a catalyst

[13] . Cationic polymerization The data from the literature clearly show that coordination polymerization and anionic polymerization are not suitable for the synthesis of PECH, mainly because of a lack of control of the molecular mass and a functionality very often very far from the target value: 2. In contrast, ring-opening cationic polymerization with a diol as an initiator leads to a dihydroxytelechelic polymer as shown in Scheme 4. Diagram 4: Polymerization of ECH Step | - Preparation of the catalytic complex HO NE + Bis 00 HOUR where ee ee VIRE TS Ï br; Step 2 — Slow addition of the monomer o HOLA0SLS ER _ A6 } St HA OCHCHz O(CHHO+CHEHO H CH CH:CH mi ” n Polymerization is often carried out in the presence of Lewis acids, such as boron trifluoroetherate (BF:OEt, [14-18], tin tetrachloride (SnCl)

[19] , triethyloxonium hexafluorophosphate (Et,O+PF5)

[20] , and 1,4-butanediyl ditriflate

[21] . Triethyloxonium hexafluorophosphate leads to PECHs with low molecular weights (Mn < 1000 g.mol-!), while butanediyl ditriflate leads to PECHs with higher molecular weights (between 3500 and 15000 g.mol-!) but with low yields. Boron trifluoroetherate and tin tetrachloride are the most widely used, often combined with a diol as a initiator, with boron trifluoroetherate providing less polydisperse polymers than those obtained with tin tetrachloride. Two patent applications [22,23] also describe the obtaining 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 (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 is no longer usable without authorization since November 22, 2017. The obsolescence of DCE, and other chlorinated solvents, is therefore foreseeable in the short to medium term. Replacing chlorinated solvents in PECH synthesis therefore requires the search for alternative synthesis routes, compatible with current environmental and toxicological regulations, while allowing the characteristics (number average mass Mn, weight average mass Mp and hydroxyl content) of polymers currently produced and implemented on an industrial scale to be maintained. There are indeed examples of solvent-free cationic polymerization of ECH described in the literature. The first example is the polymerization of ECH in the presence of Brønsted acids such as acid clays

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

[25] and tin tetrachloride. This solvent-free route, however, presents a major problem: the risk of loss of reaction control. None of the processes described in the literature are truly satisfactory with regard to current regulations. Those that could be considered acceptable under these regulations either have low yields or result in polymers whose physicochemical characteristics do not conform to those of polymers currently produced on an industrial scale. Therefore, there is a need for an alternative synthesis of PECH that is more environmentally friendly, compliant with current regulations, and 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 The invention relates to a process for the synthesis of polyepichlorohydrin which comprises: a) the reaction of epichlorohydrin with boron trifluoroetherate [BF:O(C:H5)2] in the presence of a polymerization initiator; b) the addition of a good solvent for epichlorohydrin to the reaction product obtained in step a); c) the addition of epichlorohydrin to the reaction product obtained in step b). Detailed description of the invention The invention relates to a process for the synthesis of polyepichlorohydrin by suspension polymerization. In such a process, the starting monomer is stabilized in microdroplets dispersed in a solvent. Thus, by way of example, the cationic polymerization of vinyl monomers has been described in aqueous medium

[26] . In the context of the present invention, polymerization essentially proceeds in three steps: Step | : initiation of polymerization “directly” by bringing together epichlorohydrin, boron trifluoroetherate and a polymerization initiator. Step 2: Addition of a good solvent for epichlorohydrin and start of the propagation reaction by controlled addition of epichlorohydrin until a critical degree of polymerization is reached, beyond which the polymer is no longer in solution but in suspension. Step 3: Continue the suspension polymerization by continuing the controlled addition of epichlorohydrin. 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; b) the addition of a good solvent for epichlorohydrin to the reaction product obtained in step a); c) the addition of epichlorohydrin to the reaction product obtained in step b). In some embodiments, the polymerization initiator is water, chloropropanediol or butanediol, preferably water. In some embodiments, the suitable solvent for epichlorohydrin is a nonpolar solvent such as a hydrocarbon. In some embodiments, the hydrocarbon is at least one compound selected from an alkane and a cycloalkane. In some embodiments, the hydrocarbon is selected from hexane, methylcyclohexane, dodecane, petroleum ether, and mixtures of these compounds; preferably, the hydrocarbon is methylcyclohexane. In some embodiments, the reaction in step a) is carried out in the presence of substantially equimolar amounts of polymerization initiator and epichlorohydrin. "Subtly equimolar" means that the molar ratio between the polymerization initiator and epichlorohydrin is between 0.90 and 1.10 (i.e., a deviation of 10% from equimolarity). In some embodiments, the reaction in step a) is carried out in the presence of an excess of polymerization initiator relative to boron trifluoroetherate. In some embodiments, the reaction in step a) is carried out in the presence of a good solvent for epichlorohydrin, preferably the same good solvent as that used in step b). In some embodiments, steps a) and b) are carried out simultaneously. Step c) involves a controlled addition of epichlorohydrin to the reaction product obtained in step b). It has been found that the rate and duration of the epichlorohydrin addition allow control of the exothermicity of the reaction and the characteristics of the final polymer (polydispersity, presence or absence of macrocycles in greater or lesser quantities, …). Suspension polymerization allows obtaining PECHs with controlled molar masses (between 850 g.mol- and 4000 g.mol!) which correlate perfectly with theory, and have a low polydispersity, less than or equal to 1.25. The process according to the invention also offers an advantage in terms of scale-up (pilot and / or industrial scale). Indeed, it is common that, under the ring-opening polymerization conditions described in the literature at a laboratory scale (a few grams of monomers), the polymers obtained at a larger scale exhibit degraded characteristics in terms of Mn content, polydispersity, and functionality, or that the exothermic reaction is more difficult to control. The process described here can be extrapolated to more than one hundred grams of monomer without any impact on the polymer's characteristics. In summary, the suspension polymerization process according to the present invention allows for very good control of the polymerization and offers numerous advantages: - perfect control of the temperature exotherm often observed during cationic ring-opening polymerization; - polymerization carried out in solvents less toxic than the chlorinated solvents commonly used for cationic ring-opening polymerization; - polymerization time (approximately 6 to 7 hours) compatible with an industrial scale; - polymerization yields greater than 90%, comparable to yields obtained on an industrial scale which are around 95%; - obtaining a monomodal polymer with perfectly controlled Mn (from 850 to 4000 g.mol-*) having a functionality in accordance with the theory, to be compared with a functionality of 1.4 to 1.6 for a PECH produced, to date, on an industrial scale; - low polydispersity, less than or equal to 1.25, which is therefore comparable to the values ​​measured on an industrial PECH. In addition, it is possible to recycle the good solvent used in step b). According to certain embodiments, the process of the invention further comprises: d) decantation of the product obtained in step c), followed by separation of the polyepichlorohydrin and recovery of the good residual solvent. According to some embodiments, the recovered solvent is reused in step b) or, as indicated above, in steps a) and b) combined when these are carried out simultaneously. The invention will be better understood with the aid of the following illustrative examples. 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) under the following conditions: NMR !H NMR (500 MHz) in CDCI3 at 25°C on a Bruker AC-500 SEC Equipment: Thermo Scientific Ultimat 3000 with an Agilent column PLgel 5 µm MIXED-C (300 x 7.5 mm) and a pre-column (PL gel 5 µm 50X7.5 mm) thermostatically controlled at 30°C. Detection: refractometry and UV. Eluent: THF, 1.0 ml / min. Standard: polystyrene. The polydispersity D of polyepichlorohydrin is equal to the ratio Mp / Mn. The functionality is calculated according to the formula: [Mn(SEC) / Mn(RMN)]x2. The formulas BF,O(C;H,); and BF,OEt. are used interchangeably to refer to boron trifluoroetherate (also called boron trifluoride dietherate). Example 1 0.48 mL (6.12 x 10⁷ mol) of ECH, 0.046 mL (3.72 x 10⁴ mol) of BF₂O(C:H₅), and 0.1 mL (5.56 x 10⁷ mol) of HzO were introduced into a round-bottom flask. The reaction mixture was stirred for 1.5 h at 25 °C until a clear, viscous liquid formed. Then, 17 mL of methyl cyclohexane was added to the flask, followed by the addition, using a syringe pump, of 8.1 mL (0.1 mol) of ECH, controlling the addition rate to maintain the exothermicity of the reaction. After total addition of the ECH, the reaction mixture was stirred for 1h, and the PECH was recovered after decantation and then vacuum drying at 60°C until constant weight. PECH was purified by dissolution in toluene, washing with an aqueous solution of sodium bicarbonate and then with water, evaporation of the solvent under reduced pressure, and drying of the polymer to constant weight. 10 g of PECH were thus obtained. Yield = 100%; Mn (NMR) = 1375 g.mol*; Mn (SEC) = 1480 g.mol"; D = 1.14: Functionality = 2. Example 2 3.2 mL (4.08 x 10⁷ mol) of ECH, 0.32 mL (2.69 x 10⁻³ mol) of BF:OEt, 0.7 mL (3.85 x 10⁻³ mol) of H₂O, and 3.2 mL of methyl cyclohexane were introduced into a flask. The reaction mixture was stirred for 1.5 h at 25°C until a clear, viscous liquid formed. Then, 160 mL of methyl cyclohexane was added to the reactor, followed by the addition of 81.3 mL (1.04 mol) of ECH, controlling the addition rate to maintain the exothermicity of the reaction. After complete addition of ECH, the The reaction mixture was stirred for 1.5 hours. The PECH was recovered and purified according to the procedure in Example 1. 94 g of PECH were thus obtained. Yield = 95%; Mn (NMR) = 2420 g / mol; Mn (SEC) = 2670 g / mol; D = 1.22; Functionality = 2. Example 3 The procedure from Example 1 was repeated, but with molar ratios [ECHJ / [H,O] = 27 and [H,OJ / [BF;OEt,] = 15, and by varying the nature of the suitable solvent for epichlorohydrin. The results are presented in the following table. [Tables 1] |p [solvent [Rat (%) OEM | Re [119 MnNMR |MnSEC (g.mol}) (g-mol!) 2120 2370 Hexane 100 Dodecane 98 Petroleum Ether |100 3080 2480 1.20 2190 2460 1.19 2260 2290 1.20 Bibliographical references 1) Vandenberg, EJ Award Address, Polymer 1994, 35, 49334939 2) Vandenberg, EJ Organometallic Catalysts for Polymerizing Monosubstituted Epoxides. J. Polym. Sci. 1960, 47, 486—489 3) Vandenberg, EJ Epoxide Polymers: Synthesis, Stereochemistry, Structure, and Mechanism. J. Polym. Sci. Part A: Polym. Chem. 1969, 7, 525-567 4) Brochu, S.; Ampleman, G. Synthesis and Characterization of Glycidyl Azide Polymers Using Isotactic and Chiral Poly(epichlorohydrin)s. Macromolecules 1996, 29 , 5539 — 5545, 5) Ferrier Jr, R. C.; Pakhira, S.; Palmon, S$. E.; Rodriguez, C. G.; Goldfeld. D. E.; Iyiola, O. O.; Chwatko, M.; Mendoza-Cortes, J. L.; Lynd, N. A. Demystifying the Mcchanism of Regio- and Isosclcctive Epoxide Polymerization Using the Vandenberg Catalyst. 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Claims

Demands

1. A process for the synthesis of polyepichlorohydrinc comprising: a) the reaction of epichlorohydrin with boron trifluoroetherate in presence of a polymerization initiator; b) the addition of a good solvent for epichlorohydrin to the product of reaction obtained in step a); c) the addition of epichlorohydrin to the reaction product obtained in step b).

2. A method according to claim 1, wherein the polymer initiator- Risation is water.

3. A method in any one of claims 1 and 2, wherein the good The solvent for epichlorohydrin is a hydrocarbon.

4. A process according to claim 3, wherein the hydrocarbon is at less a compound selected from an alkane and a cycloalkane.

5. A process according to claim 4, wherein the hydrocarbon is selected among hexane, methylcyclohexane, dodecane, petroleum ether and mixtures of these compounds, preferably the hydrocarbon is the me- thylcyclohexane.

6. A method according to any one of claims 1 to 5, wherein the reaction of step a) is carried out in the presence of substantially equimolar amounts of polymerization initiator and epichlorohydrin.

7. A method according to any one of claims 1 to 6, wherein the reaction of step a) is carried out in the presence of an excess of initiator of polymerization compared to boron trifluoroetherate.

8. A method according to any one of claims 1 to 7, wherein the reaction of step a) is carried out in the presence of a suitable solvent for epichlorohydrin, preferably the same good solvent as that used in step b).

9. A method according to any one of claims 1 to 8, wherein the steps a) and b) are implemented simultaneously.

10. A method according to any one of claims 1 to 9, which includes, in addition: d) decantation of the product obtained in step c), followed by separation of polyepichlorohydrin and recovery of the good residual solvent.

11. 1 A process according to claim 10, wherein the recovered solvent is reused in the process according to claim 1.