Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From heterocyclic reactant containing as ring atoms oxygen,...
Reexamination Certificate
2000-10-17
2002-03-26
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From heterocyclic reactant containing as ring atoms oxygen,...
C528S408000, C528S403000, C528S420000, C528S482000, C528S485000, C528S489000, C525S333100, C549S512000, C549S513000
Reexamination Certificate
active
06362311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to a novel method of polymerizing poly(glycidyl nitrate) from high purity glycidyl nitrate synthesized from glycerol. This invention is also directed to methods for making explosive compounds, pyrotechnics, and solid propellants comprising poly(glycidyl nitrate) elastomer binders.
2. Description of the Related Art
Solid high energy compositions, such as propellants, explosives, gasifiers, or the like, generally comprise solid particulates, such as fuel particulates and/or oxidizer particulates, dispersed and immobilized throughout a binder matrix comprising an elastomeric binder.
In recent years, energetic polymers have been developed and evaluated as replacements of inert polymer binders in cast propellant systems, explosive compositions, and pyrotechnics. The substitution of an energetic polymer for an inert polymer in a typical pressable or extrudable explosive composition increases the detonation pressures and detonation velocities of the explosive. In this regard, much recent work has centered on attempts to produce acceptable energetic polyoxetanes and glycidyl azide polymer (GAP).
A problem with elastomeric binders formed from polyoxetanes is their relatively low oxygen balance. Also, it has been reported that polyoxetanes tend to have mechanical characteristics less than that which is desirable for some high energy applications, particularly for a rocket motor propellant.
Due to safety and toxicity concerns that arise during processing of glycidyl azide monomer, GAP is commonly synthesized by polymerizing epichlorohydrin (rather than glyciyl azide) to form poly(epichlorohydrin). The chlorine substituents are then displaced by reaction with sodium azide in dimethylsulfoxide. Thus, the desire to avoid the direct polymerization of glycidyl azide complicates the GAP synthesis route. Moreover, the resulting polymers have been reported as being characterized by low molecular weights and amorphous structures.
Poly(glycidyl nitrate) (PGN) has been known and recognized as a possible energetic polymer suitable for use in propellants, explosives, gas generants, pyrotechnics, and the like. PGN is most commonly synthesized in the industry by a three-step procedure characterized by a first step in which epichlorohydrin is nitrated, and a second step in which the nitrated epichlorohydrin is recyclizated with a base to form glycidyl nitrate. The glycidyl nitrate is then polymerized in a third step by cationic polymerization to form PGN. The selection of epichlorohydrin derives from the low cost of the reagent and the relatively high nitration yields obtained by the nitration of epichlorohydrin. Despite these relatively high nitration yields, in the subsequent recyclization step an appreciable amount of epichlorohydrin is regenerated with the glycidyl nitrate. The presence of epichiorohydrin during subsequent cationic polymerization is highly disadvantageous, since the epichlorohydrin, unless removed, will copolymerize with the glycidyl nitrate to decrease the nitro group concentration of the resulting copolymer. As a consequence of the incorporation of the epichlorohydrin into the copolymer, a substantially lower energetic characteristic is attained than had epichlorohydrin not participated in the polymerization reaction. In order to increase purity of the monomer to an acceptable level for polymerization of PGN, the epichlorohydrin is distilled from the glycidyl nitrate prior to polymerization. However, because glycidyl nitrate is a primary nitrate ester and thus highly explosive, distillation of glycidyl nitrate in unsafe and unduly expensive for large scale operations.
Another known, yet less utilized process for making PGN resides in treating glycidol with nitrogen pentoxide N
2
O
5
in an inert solvent, then quenching the reaction mixture in aqueous solution, as discussed in U.S. Pat. No. 5,136,062 to Millar et al. However, as generally acknowledged in the art and taught by Millar et al., in this reaction sequence glycidol is commonly distilled prior to its nitration reaction. If the glycidol is not distilled, then glycidol oligomers will be present in the nitrated product, and will interfere with the polymerization reaction. Moreover, even when distillation is performed, there is a potential for thermally initiated autopolymerization of the undistilled glycidol unless the glycidol is distilled under vacuum at a relatively low temperature prior to nitration.
Thus, although it has been long recognized that PGN is an excellent energetic polymer candidate for such applications as propellants, explosives, and pyrotechnics, a need persists in the art for a low cost and non-hazardous synthesis route that produces glycidyl nitrate of adequate purity and sufficiently low moisture contamination to permit effective polymerization without distillation or other elevated temperature purification of the glycidyl nitrate or glycidyl nitrate precursor.
SUMMARY OF THE INVENTION
It is, therefore, an object of this invention to fulfill the long-felt need in the art outlined above by providing a method of synthesizing PGN from a glycidyl nitrate monomer precursor in which neither the glycidyl nitrate monomer precursor nor the glycidyl nitrate monomer must be subject to distillation or other elevated temperature purification prior to polymerizing the glycidyl nitrate monomer to PGN.
In accordance with the principles of this invention, the above and other objects are attained by a process comprising nitrating glycerol with at least one nitrating source in a solvent to form a nitrated glycerol solution comprising dinitroglycerin, treating the nitrated glycerol solution with at least one cyclizing agent to convert the dinitroglycerin into glycidyl nitrate, and polymerizing the glycidyl nitrate into poly(glycidyl nitrate).
One of the main advantages of this invention is the circumvention of the need for distillation or other vaporization techniques to remove nitroglycerin prior to polymerization of the glycidyl nitrate. Rather, the nitroglycerin can be carried along with the dinitroglycerin during polymerization, thus significantly reducing production and labor costs. In this manner, the glycidyl nitrate is not exposed to elevated temperatures sufficient to cause accidental explosion or deflagration of the nitrate ester. Still more preferably, the glycidyl nitrate is not heated above room temperature at any time prior to polymerization. Moreover, given the high energy performance of nitroglycerin, the nitroglycerin can optionally be retained with the PGN, i.e., not washed out, for subsequent processing and end use.
Other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims which explain the principles of this invention.
DETAILED DESCRIPTION OF THE INVENTION
It is generally known in the art that glycidyl nitrate can be hydrolyzed from dinitroglycerin, which in turn can be synthesized by the nitration of glycerol CH
2
(OH)CH(OH)CH
2
(OH) (also known and referred to herein as glycerin), as proposed by T. Davis, The Chemistry of Powder and Explosive (J. Wiley & Sons, Inc. 1943), the complete disclose of which is incorporated herein by reference. Preferably, the nitration of glycerol is performed with nitric acid as the nitrating agent. Another one of the advantages of this invention is that it is not necessary to use industrial grade pure nitric acid, i.e., 98-100 wt %; rather, 90 wt % nitric acid is suitable for this invention. It is also within the scope of this invention to use other nitrating agents, such as the following: mixed acids, such as sulfuric and nitric acids, or acetyl nitrate; nitronium ion salts, such as NO
2
BF
4
, NO
2
ClO
4
, and/or N
2
O
5
; and trifluoroacetic anhydride (TFAA) with ammonium nitrate, nitric acid, and/or Crivello reagents. The molar ratio of nitrating agent to glycerol is preferably in a range of from about 4:1 to about 5:1.
The nitration of glycerol produces the five different compounds: trinitroglyc
Cannizzo Louis F.
Hajik Robert M.
Highsmith Thomas K.
Sanderson Andrew J.
Alliant Techsystems Inc.
Sullivan Law Group
Truong Duc
LandOfFree
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