|Title of Invention||
A PROCESS FOR SYNTHESISING A HYDROXY TERMINATED GLYCIDYL AZIDE POLYMER
|Abstract||This invention relates to a process for synthesising hydroxy terminated glycidyl azide polymer having di and tri functional moieties in the same system. A boron trifluoride-polymer adduct prepared by reacting ooron trifluoride etherate with a diol and a triol is used as an initiator to polymerise epichlorohydrin. This polyepichlorohydrin is reacted with sodium azide to give glycidyl azide polymer with di and tri hydroxy terminal groups. This compound is used as a binder in solid propellants.|
This invention relates to a process for synthesising a hydroxy terminated glycidylazide polymer and is particularly but not exclusively related to the synthesis of glycidyl azide polymers having an average molecular weight of 2000 to 3000 daltons and hydroxy functionality varying from 2 to 3.
Glycidyl azide polymers with hydroxy functionality between two and three can be used as binders for solid propellants which are cured with diisocyanates after mixing with active ingredients such as fuel and oxidizer.
In space exploration and related activities, large quantities of solid propellants are required. Till now hydroxy terminated polybutadiene (HTPB) has been used as binders for metallic fuels, oxidisers and curing agents. Conventional metallic fuels like aluminium, oxidisers like ammonium perchlorate and curing agents such as diisocyanates are mixed thoroughly with the required quantity of hydroxy termianted polybutadiene binder to form a slurry and is cast in the rocket chambers. Such binders are termed as "energetic binders' as they are capable of increasing the specific impulse of solid propellants made from it. Binders with better energy giving and mechanical properties are considered superior and are in demand.
Curing of the propellant composition usually takes place due to the reaction between the terminal hydroxy groups of the binder and isocyanates. The mixture gets cured without the liberation of any by-products. It is observed that difunctional binders such as difunctional hydroxy terminated polybutadiene or difunctional glycidyl azide polymer reacts with
diisocyanate leading to chain extension and not cross linking. Cross linking is essential for the formation of three dimensional network structures with elastomeric properties in the cured propellant. Conventionally this is achieved by the addition of low molecular weight trifunctional polymers as cross-linking agents. A polymer having both trifunctional and difunctional molecules are preferred to the addition of more than one compounds to the propellant.
Glycidyl azide polymer is one of the most promising high-energy propellant binders. This polymer possesses pendant azide groups in the polymer chain which makes it highly energetic. It has a positive heat of formation (AHf = + 957 KJ/kg) which is desirable for high energy propellant binder. A composite propellant made with glycidyl azide polymer is found to be capable of delivering higher specific impulse when compared to the currently used hydroxyl terminated polybutadiene binder. Glycidyl azide polymers are also found to be more environmentally friendly when used with oxidizers like ammonium nitrate.
The curing of a difunctional GAP to an elastomer is done by reacting it with a diisocyanate in presence of low molecular weight triol like 1,1,1-trimethylol propane as cross-linking agent. However, in order to make use of GAP as a substitute for HTPB in a similar application, it is necessary that the polymer must form network structures and hence a polymer having both difunctional and polyfunctional is developed. Unlike HTPB where the hydroxyl groups in the binder and the hydroxyl groups in the cross-linking agents are primary and thus of same reactivity, more than 90% of the hydroxyl groups present in GAP are secondary in nature and thus have a
lower reactivity compared to the hydroxyl groups of the cross-linking agent which are of primary nature. In such a system the latter hydroxyls react with diisocyanates much faster than the hydroxyl groups of GAP. Before the completion of the reaction of the hydroxyl groups of GAP a portion of isocyanate may react with the moisture leading to side reactions, which results in formation of blow holes in the cured system. Thus it becomes imperative for GAP to be used as an effective propellant binders, it must have designed mix of di and tri functionality. In other words, it is necessary to have cross-linkable trifunctional units of same reactivity in the GAP itself so as to avoid addition of low molecular weight trifunctional cross-linking agents. The present invention describes the synthesis of GAP possessing both trifunctional and difunctional units.
The present invention provides a method for the synthesis of hydroxyl terminated epichlorohydrin polymer containing both di and tri hydroxyl functionality in the same system and converting the same into glycidyl azide polymer having tailor made desired functionality. The glycidyl azide polymer produced by this method has both di and poly functional moieties and can be used as binder to produce a cross linked network structure using a diisocyanate curing agents such as toluenediisocyanate, isophorae diisocyanate, methylene-bis-cyclohexylisocyanate, hexamethylenedi-isocyanate, 4,4'diphenylmethanediisocyanate and the like, without need for the addition of low molecular weight cross-linking agents.
This invention relates to a process for synthesising a hydroxy terminated glycidyl azide polymer having di and trifunctional hydroxy units which comprises the steps of preparing an initiator by reacting boron
trifluoride etherate with a diol and triol to produce a BF3-polyol complex cationically polymerising epichlorohydrin in the presence of said BF3-polyol complex to produce polyepichlorohydrin, converting the said polyepichlorohydrin to produce hydroxy terminated glycidyl azide polymer and subsequently recovering the same from the reaction mixture in a known manner. The diols such as ethylene glycol, butane diol, propane diol and triols like glycerol and methylol propane are used.
Hydroxy terminated glycidyl azide polymer may have an average molecular weight of 2000 to 3000 daltons and a functionality of 2 and 3.
Boron trifloride etherate is first reacted with a mixture of low molecular weight diol and a triol. The adduct formed is used as an initiator to polymerise epichlorohydrin. The polymerization is preferably carried out in toluene or dichloromethane medium, at a temperature of 263 to 283 K. Epichlorohydrin is added slowly to the initiator under constant stirring while maintaining the reaction temperature constant throughout the addition. The reaction is allowed to continue for some more time and then the polymerisation is quenched by the addition of distilled water to the reactor. The mixture is stirred well and is allowed to settle. Subsequently, the water layer is removed and the polymer layer is repeatedly washed with sodium bicarbonate solution followed by distilled water washing. Low molecular weight fractions are removed by washing the polymer with a mixture of isopropanol and hexane and the separated polymer is dried in vacuum. The polyepichlorohydrin thus obtained is found to have a hydroxy functionality between 2 and 3. The ratio of the functional unit may depend on the ratio of the triol and diol used in the formation of the adduct.
Polyepichlorohydrin thus obtained is converted into glycidyl azide polymer by reacting it with sodium azide in a polar solvent medium. Solvents like dimethyl formamide, dimethyl sulphoxide and dimethyl acetamide are found to be appropriate. The reaction is carried out at 353 to 383 K for about 5 to 25 hours. The reaction time is found to be inversely proportional to the reaction temperature. The reaction is complete in about 24 hours when carried out at 353 K. The reaction mixture is then cooled and the polymer is precipitated by addition of water. After removing the water layer the polymer is repeatedly washed with distilled water under constant stirring. After separating water, the polymer is dissolved in dichloromethane, water layer is further separated therefrom and the solvent dichloromethane was removed by distillation under vacuum to obtain glycidyl azide polymer with di and tri hydroxy functional groups.
1. A process for synthesising hydroxy terminated glycidyl azide polymer having di and tri functional hydroxy units comprising the steps of preparing an initiator by reacting boron trifluoride etherate with a diol and triol to produce a BF3-polyol complex cationically polymerising epichlorohydrin in the presence of said BF3-polyol complex to produce polyepichlorohydrin, converting the said polyepichlorohydrin to produce hydroxy terminated glycidyl azide polymer and subsequently recovering the same from the raction mixture in a known manner.
2. The process as claimed in claim 1, wherein boron trifluoride etherate is reacted with a mixture of low molecular weight diol and triol such as 1,2 ethylene diol, 1,4 butane diol, 1,3 propane diol, glycerol and 1,1,1 ,trimethylol propane.
3. The process as claimed in claim 1, wherein said polymerisation of epichlorohydrin is carried out at 263K to 283K in toluene or dichloromethane medium.
4. The process as claimed in claims 1 to 3 wherein epichlorohydrin is slowly added to said boron trifluoride polyol initiator under constant stirring.
5. The process as claimed in claim 4, wherein the polymerization of epichlorohydrin is quenched by adding water to the reaction mixture.
6. The process as claimed in claim 5, wherein said polyepichlorohydrin is repeatedly washed with a mixture of isopropanol and hexane to remove low molecular weight compounds therefrom and then dried in vacuum.
7. The process as claimed in any of the preceding claim wherein the said polyepichlorohydrin is reacted with sodium azide in polar solvent medium such as dimethylformamide, dimethylsulphoxide and dimethyl acetamide to produce said glycidyl azide polymer.
8. The process as claimed in claim 7, wherein said reaction is carried out at 353 to 383K for 5 to 25 hours.
9. The process as claimed in claim 7 and 8 wherein said glycidyl azide polymer is precipitated by addition of water to the reaction mixture and is subsequently washed with water.
10. The process as claimed in claims 7 to 9 wherein said glycidyl azide
polymer is purified by dissolving the same in dichloromethane,
washing and subsequently removing the solvent therefrom.
11. A process for synthesising hydroxy terminated glycidyl azide polymer
substantially as herein described.
|Indian Patent Application Number||856/MAS/2000|
|PG Journal Number||26/2007|
|Date of Filing||10-Oct-2000|
|Name of Patentee||M/S. INDIAN SPACE RESEARCH ORGANISATION|
|Applicant Address||ANTARIKSHA BHAVAN,NEW BEL ROAD, BANGALORE-560 094.|
|PCT International Classification Number||C07C247/04|
|PCT International Application Number||N/A|
|PCT International Filing date|