Title of Invention

"ENERGETIC BINDER (AZIDO POLYMER)."

Abstract

An energetic binder produced from reaction between azido polymer and multifunctional dipolarophiles that are highly electron deficient, where in the binder produced exhibits high energy out puts and high char yields, wherein the azido polymer used is such as glycidyl azide polymer (GAP), poly allyl azide (PAA), poly (bis-azidomethyl oxetane [poly (BAMO)] or poly (azidomethyl methyloxetane [poly (AMMO)]and dipolarophiles used is selected from poly imides.

Full Text

The present invention relates to energetic binder. The invention particularly relates to high energetic binder based on azido polymers, and novel dipolarophiles. More particularly the binder, of the present invention, is based on glycidyl azide polymer or novel poly (allyl azide) and highly electron deficient dipolarophiles. The binder finds its use as high-energy material and fuel in rocket technology. Particularly they are used as high-energy binder in composite solid propellant. High-energy solid rocket propellants, currently in use, are composite materials having a binder [hydroxy terminated polybutadiene (HTPB)], high-energy additives [e.g. ammonium per chlorate (AP)] and pyrolants (metallic powder). HTPB is an inert binder, which has been used in cast-cure propellant system. Substitution of HTPB by a more energetic binder may lead to an upgradation in performance of such propellants. AP, the high-energy additive, has its own inherent disadvantages, as it produces chlorine rich combustion products (30%), which have potential environmental implications. A reference can be made to Aggarwal J. P.; Walley S. M.; Field J. E. J. "Propulsion and Power"1997,13 (4),463. Further, it produces white smoke trails, which are disadvantageous for specific applications demanding smokeless plume. Ammonium nitrate (AN) has long been considered a highly desirable oxidizer for solid-fuel rocket propellants because of its extremely low cost, low sensitivity, low signature and absence of halogens. However, it has a crystalline phase stability problem that causes unpredictable ballastic performance in some cases and catastrophic rocket motor failure in others. This has limited the use of AN without the phase stabilizers [Borman S. Military Technology 1994,72 (3),18]. A new generation of propellants is being developed worldwide these days. The operational trends for future applications of these energetic materials are to improve performance, satisfy insensitive munitions, comply with environmental aspects, and reduce costs. The use of energetic additives, mainly binders and plasticisers, is considered to be one of the practical ways to improve the energy level and other technical performances of solid propellants. Recent advances in propellants research, therefore, are aimed at developing high energy binders which give better performance than the commonly used HTPB and which are compatible with the eco-friendly oxidizers ammonium nitrate (AN), hydrazinium nitroformate (HNF), or ammonium dinitramide (ADN). Azido containing compounds and polymers are important in the field of propellants since the azido group is highly energetic and contributes a positive heat of formation of 313-397 kJ/mole. Further the highly energetic azido group can be easily incorporated into a polymer or oligomer at high weight percentage loading. A useful class of azido polymers are oligomers, polymers or copolymers described as azido-substituted polyethers. These polymeric azides include glycidyl azide polymer (GAP) and its copolymers, poly (bis-azidomethyl oxetane) [poly (BAMO)] and its copolymers, and poly (azidomethyl methyloxetane) [poly (AMMO)]. These polymers contain azide groups along the polymer chain as pendant groups, which make them highly energetic. The exothermic scission of these -N3 bond releases energy of the order 685 kJ/mole. Generally, the product of polymerization is a relatively low molecular weight polymer or oligomer having average molecular weight between 500 and 25000 or high molecular weight with molecular weight between 25,000 and 1,00,000. See US Patent In applications where these azide polymers are used as high energy mterials, it is typical for these polymers to be mixed and processed into a liquid suspension containing various useful particles. The azido polymers can be further cross linked to form a solid material for easy storage and handling. Traditionally, the hydroxy-functional azido polymers having Mn The traditional method used for propellants formulation is to mix liquid GAP polymer (Mn because the cross-links are irreversibly covalent chemical bonds and thus recovery of energetic ingredients and binders is not complete. Therefore, an elastomeric GAP with Mn>1.4 x 105 has been developed to overcome this problem. The synthesis and use of recyclable thermoplastic elastomer (TPE) based on azido polymers is gaining importance in the field of energetic binders. The other drawback of the use of poly isocyanate as curing agent is its susceptibility to the interference by the presence of moisture. The moisture inhibits the curing process. The another drawback is that the extent of cross linking is limited by stoichiometric factors when cross linked with multi functional isocyanate. An azido polymer can only be reacted with isocyanate at terminal hydroxy groups and thus poses problems to obtain a desired product. Further, the decomposition products of cured GAP contain highly toxic HCN, which need to be suppressed and the To of GAP increases on curing that has to be lowered in order to develop energetic binder. US Patent No. 5,681,904 teaches use of multi-functional dipolarophiles such as acrylic esters, acrylic amides, acetylenic esters, acetylenic amides or mixture thereof to cross link azido polymer. The polymers used include linear or branched Glycidyl Azide polymers (GAP) such as diols, polyols, and plasticizers; BAMO and AMMO. These polymers are promising candidates for the energetic binders having minimum smoke, reduced pollution and sensitivity. In addition to being fuel rich, these propellants liberate large amounts of H2, N2, CO and gaseous hydrocarbons on burning and provide high burning rate. There is no reference to the use of allyl azide for the preparation of energetic binder. This is the first time; a novel allyl azide has been used for the preparation of high energetic binder. The other new findings of this invention are the process of azidation and use of novel dipolarophile curing agent. The novel dipolarophile being highly electron deficient helps increasing reaction rate with azido group. Thus either the new curing agent or new starting material along with new curing agent is required to get high energetic binder. The main object of the present invention is to provide an energetic binder having high burn rate. Another object is to have a binder with elastomeric characteristics. Still another object of the present invention is that the binder should be without any voids. Yet another object is that the binder should have high energy out put and high char yields. Still yet another object is that the production of binder should be possible under mild conditions at reasonable rate without compromising the quality. The above objectives are possible with the curing of azido polymers such as Poly allyl azide or glycidyl azide polymers or BMMO or AMMO with highly electron deficient addition polyimides. Poly (allyl azide) (PAA) can be conveniently prepared by polymerization of low molecular mass allyl chloride followed by azidation. However, allyl chloride, during free radical polymerization undergoes degradative chain transfer yielding polymers of relatively low molecular masses. Poly (allyl chloride) having molecular masses in the range of 2000 g/mole could be obtained by following the cationic route. Allyl chloride, is polymerized using Lewis acids such as anhydrous TiCU / FeCh / AICI3 and aluminum powder, to yield polymer having molecular weight between 1000 and 3000. The azidation of poly (allyl chloride) is carried out using sodium azide and aprotic polar solvent exemplified but not restricted to dimethyl sulphoxide, dimethyl formamide, dimethyl acetamide as a solvent at 100°C for 12hrs. In addition to using curing agent such as acrylic and or acetylenic esters as disclosed in US Patent No. 5,681,904, use of Ethylene Glycol Di-Methacrylate (EGDMA) has been reported in the paper titled "Thermal Behaviour of Poly (Allyl Azide)" by B. Gaur et al likely to be published in the Journal of Thermal Analysis and Colorimetry Vol. 71 (2003) PP467-479. However, the reaction is typically hindered by the presence of the solvent. The novelty of the process of this invention is to use novel allyl azide oligomer having molecular weight in the range of 1500 to 3000g/mol. The azidation process is carried out using aprotic polar solvent selected from, but not limiting to, DMSO, DMF, and DMAC. However, other azido polymers such as GAP, AMMO or BAMO also can be used with dipolarophiles as curing agent to get high energetic binder. Further the curing agent i.e. dipolarophiles is selected from imides containing P, S, aliphatic methylene units having C ranging from 2 to 8 as curing agent. The preferred imides are bismaleimide of hexamethylenediamine (HMDA) or bis (4,4'-maleimidophenyl) sulphone or bismaleimide of diaminodiphenyl sulphone (DADPS), bis (4,4'-maleimidophenyl) ether, (3,3'-maleimidophenyl)methyl phosphine oxide. The imide is having advantage over EGDMA in flexibility of cured product and high char yield. The curing is carried out at a temperature not exceeding 60*'C in order to prevent the binder from getting brittle. Accordingly the present invention provides an energetic binder produced from reaction between azido polymer and multifunctional dipolarophiles that are highly electron deficient, where in the binder produced exhibits high energy out puts and high char yields. One of the embodiment of the present invention is that the azido polymer used may be such as glycidyl azide polymer (GAP), poly allyl azide (PAA), poly (bis-azidomethyl oxetane [poly (BAMO)] or poly (azidomethyl methyloxetane [poly (AMMO)]. Other embodiment of the present invention is that the binder contains 1 to 1.2 azido groups per 100 g of polymer used Another embodiment of the present invention is that the azido polymer used may have molecular weight in the range of 900 to 4000 preferably between 1500 and 2000 g per mol. Yet another embodiment of the present invention is that the multifunctional, highly electron deficient dipolarophile used may be such as polyimides used are the one containing P, S, and/or aliphatic methylene units having carbon ranging from 2 to 8. Still another embodiment of the present invention is that the imide used may be bismaleimide of hexamethylenediamine (HMDA) or bis (4,4'- maleimidophenyl) sulphone or bis maleimide of diaminodiphenyl sulphone (DADPS), bis (4,4'-maleimidophenyl) ether, (3.3'-maleimidophenyl)methyl phosphine oxide. Still yet another embodiment of the present invention is that the amount of imide used may vary from 10 to 30 phr. Further the energetic binder of this invention may exhibit the heat liberation to the tune of > 800 J/g. The energetic binder according to this invention may be capable of heat liberation ranging from 800 to 1350 J/g. The residual weight % of the binder as claimed in this application, in nitrogen atmosphere at 6OO0C, may be in the range of 13 to 26 preferably 19 to 23. The binder is prepared by the process as described in our co-pending patent application No. 1316/DEL/2002. However, though the azido polymer used may be such as GAP, Poly (BAMO) or Poly (AMMO) the process is only exemplified by Poly allyl azide. The binders were prepared by using various combinations of azido polymers and curing agents in varied proportions. High energy out put being the important aspect of the binder of the present invention, extensive studies on the energy liberation were carried out. The process was monitored by differential scanning calorimeter (DSC). Thermal stability of the binder was also evaluated by thermo gravimetric analysis. The results of the analyses are presented in the following tables. TABLE-1 Monitoring of residual cure by DSC in isothermally cured PAA using Bismaleimide of HMDA (hexamethylenediammine) (10-30 phr) at 40 C and 60°C (heating rate 10°C/min.). TABLE REMOVED) Samples were kept at 40 C (2 days) before keeping at 60 C. TABLE-2 Thermal behaviour of isothermally cured PAA with 10-30 phr of Bismalemide of HMDA (hexamethylenediamine) (heating rate 5 C/min.). (TABLE REMOVED) TABLE-3 Monitoring of residual cure by DSC in isothermally cured PAA using Bismaleimide of DADPS (diaminodiphenylsulphone) (15 phr) at 40°C and 60°C (heating rate 10°C/min.). (TABLE REMOVED) Sample was kept at 40°C (2 days) before keeping at 60°C. TABLE-4 Thermal behaviour of isothermally cured PAA with 15 phr of Bismaleimide of DADPS (diaminodiphenysulphone) (heating rate 5°C/min.). (TABLE REMOVED) Sample was kept at 40 C (2 days) before keeping at 60 C. TABLE-5 Monitoring of residual cure by DSC in isothermally cured PAA using Bismaleimide of DADPE (diaminodiphenylether) (10-30 phr) at 40°c and 60°C (heating rate 10°C/min.). (TABLE REMOVED) Sample was kept at 40°C (2 days) before keeping at 60°C. TABLE-6 Thermal behaviour of isothermally cured PAA with 10-30 phr of Bismaleimide of DADPE (diaminodiphenylether) (heating rate 5°C/niin.). (TABLE REMOVED) ADVANTAGES 1. The product is efficient. 2. The product has excellent elastomeric characteristics. 3. The product acts as a high-energy binder. 4. The product is devoid of bubbles. 5. The product has improved burn rate. 6. The product has high energy out put. 7. The product has high char yield. 8. The product can be obtained by an economical, eco friendly process that does not require stringent conditions. WE CLAIM: 1. An energetic binder produced from reaction between azido polymer having molecular weight in the range of 900 to 4000 and multifunctional dipolarophiles that are highly electron deficient, wherein the dipolarophiles used varies from 10 to 30 phr and where in the binder produced exhibits high energy out puts and high char yields. 2. The energetic binder according to claim 1, wherein the azido polymer such as glycidyl azide polymer (GAP), poly allyl azide (PAA), poly (bis-azidomethyl oxetane [poly (BAMO)] or poly (azidomethyl methyloxetane [poly (AMMO)] is used. 3. The energetic binder according to claim 1, wherein the binder contains 1 to 1.2 azido groups per 100 g of polymer used. 4. The energetic binder according to claim 1, wherein the azido polymer used has molecular weight in the range of 1500 to 2000 g per mol. 5. The energetic binder according to claim 1, wherein the multifunctional, highly electron deficient dipolarophile used is such as polyimides used are the one containing P, S, and/or aliphatic methylene u-nits having carbon ranging from 2 to 8. 6. The energetic binder according to claim 1 and 4, wherein the imide used is bismaleimide of hexamethylenediamine (HMDA) or bis (4,4'-maleimidophenyl) sulphone or bis maleimide of diaminodiphenyl sulphone (DADPS), bis (4,4'-maleimidophenyl) ether, (3.3'-maleimidophenyl)methyl phosphine oxide. 7. The energetic binder according to claim 1,'where in the heat liberation exhibited is > 800 J/g. 8. The energetic binder according to claim 1, where in the heat liberation exhibited ranges from 800 to 1350 J/g. 9. The energetic binder according to claim 1, where in the residual weight % in nitrogen atmosphere at 600 C ranges from 13 to 26 preferably 19 to 23. 10.The energetic binder substantially as herein described.

Documents:

725-DEL-2003-Abstract-(18-07-2011).pdf

725-del-2003-abstract.pdf

725-DEL-2003-Claims-(18-07-2011).pdf

725-del-2003-claims.pdf

725-DEL-2003-Correspondence Others-(18-07-2011).pdf

725-del-2003-correspondence-others.pdf

725-del-2003-description (complete).pdf

725-del-2003-form-1.pdf

725-del-2003-form-18.pdf

725-del-2003-form-2.pdf

725-DEL-2003-Form-5-(18-07-2011).pdf

725-del-2003-gpa.pdf