Patent Application
20240392067
The invention relates to the field of energetic materials. More specifically, the invention concerns a process for synthesizing a polyglycidyl azide intermediate, namely polyepichlorohydrin.
With the aim of increasing the ballistic performance of tactical and strategic missiles, more energetic materials have been developed, in particular using glycidyl polyazide (GPA) to replace the inert binders historically used, such as polybutadienehydroxytelechelic (PBHT).
GPA can be produced in two stages, as shown in Scheme 1 below, from epichlorohydrin (ECH) via polyepichlorohydrin (PECH), which is a dihydroxytelechelic polymer.
In the literature, there are three main methods of polymerising ECH to obtain PECH:
Catalytic ring-opening polymerisation of ECH was first described by Vandenberg [1-4] to synthesise PECHs with high molecular weights (Mn≥50,000 g·mol−1).
More recently other active species have been described such as bis(μ-oxo)dialkylaluminum [5]. Several other monometallic [6-8] and bimetallic catalyst systems have also been described, but again for the synthesis of high molecular weight PECHS.
Generally speaking, coordination polymerisation has a number of drawbacks from the point of view of understanding the mechanisms involved:
A more recent publication describes the solvent-free polymerisation 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. Yields ranged from 30 to 84% for number average weights of 900 g·mol−1 to 4,200 g·mol−1 with, however, a high polydispersity of the order of 1.5.
The controlled anionic polymerisation of ECH in the presence of Oct4NBr/(iBu)3Al as initiator has been described by Carloti [11-12]. It has a number of advantages, including the use of a non-chlorinated solvent such as toluene. However, it also has one major drawback, which is the production of a monohydroxyl polymer, as shown in scheme 3 below.
Very recently, direct polymerisation of glycidyl azide has been carried out using triethylborane combined with tetrabutylammonium bromide as a catalyst [13].
The data in the literature clearly show that coordination polymerisation and anionic polymerisation are not suitable for the synthesis of PECH, mainly because of a lack of control of the molecular weight and functionality which is very often far from the target value: 2.
In contrast, cationic ring-opening polymerisation with a diol as initiator leads to a dihydroxytelechelic polymer as shown in scheme 4.
Polymerisation 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 low molecular weight PECHs (Mn<1,000 g·mol−1), while butanediyl ditriflate leads to higher molecular weight PECHs (between 3,500 and 15,000 g·mol−1) but in 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 polymerisation.
The solvents most commonly used for ECH polymerisation are chlorinated solvents, such as methylene chloride or 1,2-dichloroethane (DCE). The use of such solvents is affected by European regulation 1907/2006, better known as REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals), which lists the substances whose use is subject to authorisation. For example, DCE has been included in Annex XIV of the REACH regulation since 14 Aug. 2014, and can no longer be used in the absence of authorisation since 22 Nov. 2017. The obsolescence of DCE, and of other chlorinated solvents, is therefore foreseeable in the short to medium term.
Replacing chlorinated solvents in PECH synthesis therefore involves finding alternative synthesis routes that are compatible with current environmental and toxicological regulations, while maintaining the characteristics (number average mass Mn, weight average mass Mw and hydroxyl content) of the polymers currently produced and used on an industrial scale.
There are certainly examples of solvent-free cationic polymerisation of ECH described in the literature. The first example is the polymerisation of ECH in the presence of Bronsted acids such as acid clays [24]. In this case, polymerisation is carried out solvent-free 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 paratoluenesulphonic acid and tin tetrachloride. However, a major problem with this solvent-free route is the risk of losing control of the reaction.
The possibility of obtaining PECH in a non-chlorinated solvent was investigated using butanediol as a polymerisation initiator and boron trifluoroetherate as a catalyst. However, this butanediol/boron trifluoroetherate system has several drawbacks:
None of the processes described in the literature is therefore really satisfactory in terms of current regulations. Those that could be considered acceptable with regard to these regulations have low yields or lead to polymers whose physico-chemical characteristics are not in line with those of polymers currently produced on an industrial scale.
There is therefore a need for an alternative synthesis of PECH that is more environmentally friendly, compatible with current regulations, and that does not alter the physico-chemical properties of this product. It was with these specifications in mind that the present invention was developed.
The invention relates to a process for the synthesis of polyepichlorohydrin which comprises:
In the context of the present disclosure, the expression “reaction product” has the usual and common meaning used in chemical synthesis, namely a product which results from the reaction between at least two reagents which interact and are transformed into said product. Thus, the expression “reaction product obtained in step x” is equivalent to the expression “product obtained at the end of step x”. It will be further noted that when a process described in the present disclosure comprises a plurality of steps, each step is distinct. Thus, if a process comprises a step a) and a step b) involving “the reaction product obtained in step a)”, it goes without saying for those skilled in the art that step b) cannot begin until step a) has been completed, i.e. the reagents have been consumed to form the “reaction product from step a)”.
The invention relates to a process for synthesising polyepichlorohydrin which implements cationic polymerisation of epichlorohydrin by ring opening according to a so-called “activated monomer” mechanism. In this mechanism, shown in scheme 5, the chain ends are neutral and propagation takes place via nucleophilic attack of a hydroxyl group on the oxonium ion present in the monomer, thus forming only a linear diol PECH.
In order to control the molar weight of PECH, the polymerisation essentially proceeds as a two-step process:
The polymerisation termination phase proceeds in the conventional way in the presence of water.
Thus, the present invention relates to a process for the synthesis of polyepichlorohydrin which comprises:
In some embodiments, the polymerisation initiator is water, butanediol or 3-chloro-1,2-propanediol, preferably water.
In some embodiments, step a) is carried out in the absence of solvent.
In some embodiments, step a) is carried out in the presence of a non-chlorinated solvent.
Advantageously, the non-chlorinated solvent is toluene, acetonitrile or nitromethane, preferably toluene.
In some embodiments, the polymerisation initiator and epichlorohydrin are used in substantially equimolar quantities in step a).
In some embodiments, the polymerisation initiator is used in excess relative to boron trifluoroetherate in step a).
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).
In some embodiments, epichlorohydrin is added in one or several stages in step b).
In some embodiments, the reaction of step a) is controlled to obtain an epichlorohydrin oligomer having a degree of polymerisation (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.
The process according to the invention is compatible with a scale-up (pilot and/or industrial scale). Indeed, this process makes it possible to obtain polyepichlorohydrin on a scale of a hundred grams (see examples 4 and 6) without degrading the characteristics of the polymer in terms of Mn, polydispersity and functionality, or any risk associated with the exothermicity of the reaction.
To sum up, the synthesis process of the invention allows very good control of polymerisation and has many advantages:
The invention will be better understood with the aid of the following examples, given by way of illustration. In these examples, the number average molar mass (Mn) and weight average molar mass (Mw) of polyepichlorohydrin were determined either by NMR or by steric exclusion chromatography (SEC) using the following apparatus:
The polydispersity Ð of polyepichlorohydrin is equal to the ratio Mw/Mn.
The functionality is calculated according to the formula: [Mn(SEC)/Mn(NMR)]×2.
The formulae BF3O(C2H5)2 and BF3OEt2 are used interchangeably to designate boron trifluoroetherate (also known as boron trifluoride dietherate).
a) 0.48 mL (6.12×10−3 mol) of ECH, 0.046 mL (3.72×10−4 mol) of BF3O(C2H5)2 and 0.1 mL (5.56×10−3 mol) of H2O were placed in a round-bottom flask. The reaction mixture was stirred at 25° C. for 1.5 h until a clear viscous liquid formed. A mixture of 11.3 mL (0.15 mol) of ECH and 5.65 mL of toluene was then added via a syringe pump, controlling the rate of addition to control the exothermicity of the reaction.
b) After complete addition of the ECH, the reaction mixture was stirred for 1 h, then hydrolysed by the addition of 2 to 3 mL of distilled water. The reaction medium was diluted with toluene (about 5 mL), washed with about 50 ml of an aqueous sodium bicarbonate solution (5% by weight) and several times with distilled water (about 50 mL in total) until the washing phases were neutral. The solvent was evaporated under vacuum on a rotary evaporator and the polyepichlorohydrin obtained was dried under vacuum at 60° C. to constant weight.
Yield ≥97%; Mn (NMR)=2500 g·mol−1; Mn (SEC)=2600 g·mol−1; Ð=1.1/1.2; Functionality=2.
The procedure of Example 1 was repeated using 12.7 mL (0.17 mol) of ECH, 0.054 mL (0.44×10−3 mol) of BF3OEt2 and 1.84 mL (6.54×10−3 mol) of 3-chloro-1,2-propanediol.
Yield=94%; Mn (NMR)=2340 g·mol−1; Mn (SEC)=2370 g·mol−1; Ð=1.20; Functionality=2.
The procedure of Example 1 was repeated using pure ECH instead of ECH in solution in toluene in the second part of step a).
Yield=99-100%; Mn (NMR)=2270 g·mol−1; Mn (SEC)=2270 g·mol−1; Ð=1.23; Functionality=2.
3.2 mL (4.08×10−2 mol) of ECH, 0.33 mL (2.71×10−3 mol) of BF3OEt2, 3.2 mL of toluene and 0.73 mL (4.05×10−2 mol) of H2O were placed in a round-bottom flask. The reaction mixture was stirred for 1.5 h at 25° C. until a clear viscous liquid formed. A mixture of 80.7 mL (1.03 mol) of ECH and 37 mL of toluene was then added to the flask in two stages, the rate of addition being controlled each time to control the exothermicity of the reaction. The cumulative addition time of the ECH solution was approximately 9 h. Once the ECH solution had been added, the reaction mixture was stirred again for 1 h and then hydrolysed. Washing and recovery of the polyepichlorohydrin were carried out according to the procedure of Example 1.
Yield=97%; Mn (NMR)=2430 g·mol−1; Mn (SEC)=2580 g·mol−1; Ð=1.18; Functionality=2.
An ECH oligomer was prepared from 12.8 mL (4.08×10−2 mol) of ECH, 0.33 mL (2.71×10−3 mol) of BF3OEt2, 15.4 mL of toluene and 0.73 mL (4.05×10−2 mol) of H2O, with stirring for 4 h. The product obtained had the following characteristics:
Yield=85%; Mn (SEC)=622 g·mol−1; Mn (NMR)=425 g·mol−1: Ð=1.09; DPn=4.
A polymerisation reactor was then charged with 12.64 g (2.97×10−2 mol) of the ECH oligomer, 37 mL of toluene and 0.27 mL (2.19×10−3 mol) of BF3OEt2. The reaction medium was stirred for 1 h, then 71 mL (0.91 mol) of ECH were added to the reactor. The reaction medium was again stirred for 1 h and then hydrolysed. Washing and recovery of the polyepichlorohydrin were carried out according to the procedure of Example 1.
Yield=99%; Mn (NMR)=2500 g·mol−1; Mn (SEC)=2800 g·mol−1; Ð=1.21; Functionality=2.
3.2 mL (4.08×10−2 mol) of ECH, 0.32 mL (2.69×10−3 mol) of BF3OEt2, 3.2 mL of toluene and 0.7 mL (3.85×10−2 mol) of H2O were placed in a round-bottom flask. The reaction mixture was stirred for 1.5 h. 78 mL (1.00 mol) of ECH was then added in two stages to the flask, controlling the rate of addition each time to control the exothermicity of the reaction. The cumulative ECH addition time was about 8 h. Once the ECH solution had been added, the reaction mixture was stirred again for 0.5 h and then hydrolysed. Washing and recovery of the polyepichlorohydrin were carried out according to the procedure of Example 1.
Yield=99%; Mn (NMR)=2490 g·mol−1; Mn (SEC)=2820 g·mol−1; Ð=1.21; Functionality=2.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2109891 | Sep 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2022/051773 | 9/21/2022 | WO |
